Grade 8 Learning Module in Science - Complete

Compilation by Ben: r_borres@yahoo.com

GRADE 8
Learning Module

SCIENCE
(Qtr 1 to 4)

UNIT 1
Force, Motion, and Energy

3
FORCES AND MOTION
Overview
In Grade 7, you described an object’s motion in terms of displacement, speed
or velocity, and acceleration. You performed activities wherein you interpreted or
created visual representations of the motion of objects such as tape charts and
motion graphs. The concepts were arrived at by studying examples of uniform
motion or objects moving in straight line at constant speed. Then you were also
introduced to non-uniform motion where the object covers unequal distances or
displacements at equal intervals of time. When a jeepney starts moving, it speeds
up. When a jeepney nears a stop sign, it slows down. The jeepney is covering
different displacements at equal time intervals and hence it is not moving at a
uniform velocity. In other words, the jeepney is accelerating.
Most of the motions we come across in our daily life are non-uniform and the
primary cause of changes in motion is FORCE. In this module, you will learn about
the effects of force on motion. Newton’s Three Laws of Motion – the central
organizing principle of classical mechanics – will be presented and applied to real-life
situations.
At the end of Module 1, you will be able to answer the following key
questions:
Do forces always result in motion?
What are the conditions for an object to stay at rest, to keep moving at
constant velocity, or to move with increasing velocity?
How is force related to acceleration?
Unit 1
MODULE
1
Suggested time allotment: 8 to 10 hours

4
In the lower grades, you learned that an object can be moved by pushing or
pulling. In physics, this push and pull is referred to as force (F). Consider a ball on
top of a table as shown in Figure 1. If someone pushes the ball, it will move or roll
across the surface of the table (Figure 1a). And when it is again pushed in the
direction of its motion, it moves farther and even faster (Figure 1b). But when you
push it on the other side instead, opposite to the direction of its motion, the ball may
slow down and eventually stop (Figure 1c). Lastly, when you push it in a direction
different from its original direction of motion, the ball also changes its direction
(Figure 1d). Force therefore can make objects move, move faster, stop, or change
their direction of motion. But is this always the case? Can force always bring about
change in the state of motion of an object?
Balanced and Unbalanced Forces
An object may be acted upon by several forces. For example, an object may
be pushed and pulled in different directions at the same time. To identify which of
these forces would be able to cause change in the motion of the object, it is
important to identify all the forces acting on it.
To accurately describe the forces acting on an object, it is important for you to
be familiar first with the following terms: magnitude, direction, point of application,
and line of action. Forces are described in terms of these properties. Magnitude
refers to the size or strength of the force. It is commonly expressed in Newton (N).
Consider the diagram in Figure 2 showing a force, represented by the arrow, acting
on a ball. The direction of the arrow indicates the direction of the force while the
a.
b.
Figure 1. Effect of force on an object
c.
d.

5
length of the arrow represents the relative magnitude of the force. If the force applied
on the ball is doubled, the length of the arrow is increased two times. The line of
action is the straight line passing through the point of application and is parallel to
the direction of the force.
Activity 1
Forces on objects at rest
Objectives:
After performing this activity, you should be able to identify the forces acting
on an object at rest.
Materials:
pen pair of scissors
string book
Procedure
Situation 1
1. Hang a pen by a piece of string as shown in Figure 3a.
Q1. Is the pen at rest or in motion?
Figure 3a. Hanging pen
Figure 2. Force acting on a ball
Line of action
Point of
application
Line of action
F
Points to the
direction of the
force

6
Q2. Are there forces acting on the pen? If yes, draw the forces. You may use
arrows to represent these forces.
2. Cut the string with a pair of scissors.
Q3. What happens to the pen? What could have caused the pen’s motion?
Situation 2
1. Place a book on top of a table as shown in
Figure 3b.
Q4. Is the book at rest or in motion?
Q5. Are there forces acting on the book? If yes,
draw the forces acting on the book.
2. Let one member of your group push the book
in one direction and another member push it
in the opposite direction at the same time with
the same amount of push (force).
Q6. Did the book move? How will you make the
book move?
In the situations above, both the pen and the book are at rest. But this does
not mean that there are no forces acting on them. So what causes them to stay in
place? Consider the next activity.
Activity 2
Balance of forces
Objectives:
After performing this activity, you should be able to:
1. examine the conditions when two forces balance, and
2. explain the effect of balanced forces on the state of motion of an object.
Figure 3b. Book on a table

7
Materials:
4 sets spring balance
1 piece of sturdy cardboard
threads
Procedure:
1. Bore four holes around the cardboard as
shown. Label the holes A, B, C, and D.
2. Attach threads to the holes.
3. Attach a spring balance to thread A and another one to thread D. Hold the
cardboard to keep it still. Pull the balances along the same line such that when
released, the cardboard remains at rest.
4. When the cardboard is at rest, examine the magnitudes and directions of the
two forces by reading the spring balance.
5. Draw the line of action of the forces acting on the cardboard. Extend the lines
until they intersect. Mark the point of intersection and draw arrows starting at
this point to represent the forces acting on the cardboard.
6. Repeat steps 3 to 5 for pair B and C.
Q7. When the cardboard is at rest, how do the magnitudes and directions of the
pair of forces acting on it compare?
7. Now here is a challenge. Find out the directions of all the forces such that when
all the threads were pulled with the same amount, the cardboard will not move
or rotate when released.
Q8. If you draw the lines of action of all the forces acting on the board and extend
the lines, what will you get?
___________________________________________________________________
Figure 4

8
The diagram in Figure 5 shows the forces acting on the a) pen and b) book in
Activity 1. You learned in lower grades that all objects fall down because gravity
pulls on them towards the center of the earth. But what makes the pen and the book
stay at rest? The pen stays in place because of another force that acts on it that is
supplied by the string which we refer to in physics as tension force (T). The book, on
the other hand, stays at rest because of the upward push exerted on it by the table
which we refer to as normal force (Fn). Both the tension force and normal force
counteract the pull of gravity (Fg) that acts on the objects. Study the diagram. How
do the lengths of the arrows in each case compare? How do the magnitudes and
directions of the pair of forces compare?
In both cases, we can infer that the objects remained at rest because the
forces acting on them are equal in magnitude and in opposite directions and they lie
along the same line of action (Figure 5). The forces are balanced. This was also
demonstrated in Activity 2. Also, if you try out step 7 in Activity 2, you will find that the
lines of action of the four forces intersect through a single point. This also explains
why the body does not move or rotate.
Unbalanced Forces
If you cut the string connected to the pen, the pen will fall. Or if you push the
book on one side across the table, the book will move but will not continue moving if
you don’t continuously push it. The pen falls down because there is no more force
acting on it to counteract the pull of gravity. The book moves because of the push
that you applied. In other words, the forces acting on these objects are no longer
Figure 5: Force diagram
Force of
gravity
Normal
force
Book
(b) Book(a) Pen
Force of
gravity
Tension
force
Pen
Line of action

9
balanced. If an object initially at rest is under an unbalanced force, it moves in the
direction of the unbalanced force.
How about if the object is already in motion, how will the unbalanced force
affect its motion?
Place a ball on the desk then push it gently to one side. Observe the motion
of the ball as it rolls down the desk. What makes the ball stop rolling after sometime?
Again, you need to identify the forces acting on the ball. You can see in Fig. 6 that
the force of gravity and the normal force are again acting on the ball. But these
forces are balanced, and so the ball stays on top of the desk. However, there is
another force that acts on the ball along the horizontal line or along the force that set
the ball in motion. Do you still remember your lesson on friction in the lower grades?
You learned that friction is a force that acts between surfaces that are in contact with
one another. Friction in general acts opposite the direction of motion. In the case of
the rolling ball, the frictional force acts between the surfaces of the ball and the desk
and slows down the motion of the ball.
As the ball rolls to the right as shown in Figure 6, friction acts to the left to
retard its motion. Since you did not push the ball continuously there is no force
present to balance the force of friction. So the ball slowed down and eventually
stopped.
Again, due to the unbalanced force, the object changes its state of motion
hence we say that it accelerates. Note that acceleration is not just an increase in
velocity, but also a decrease in velocity.
Combining Forces
When we combine or add forces to determine the net or unbalanced force,
we will limit our discussion to those forces which act along the same line of action.
The algebraic signs + and – are used to indicate the direction of forces. Unlike signs
are used for forces acting in opposite directions, like in the case of the book lying on
Figure 6. Forces acting on a rolling ball
Ff
Fn
Fg

10
the table. The force of gravity (Fg) and normal force (Fn) are assigned opposite signs
- Fn is given a positive (+) sign while Fg is given a negative (-) sign. If both Fg and Fn
are given a magnitude value of 3 units, then the net force along this line (vertical) will
be:
Fnet = Fn + Fg
= 3 units + (-3 units)
= 0
If the sum of the forces equate to zero, they are considered balanced. If the
algebraic sum is not equal to zero, the forces are not balanced. The non-zero sum is
the net or unbalanced force. This unbalanced or net force would cause a change in a
body’s state of motion.
Concept check:
Study the illustrations and answer the questions that follow.
1. A boy and a girl are pulling a heavy crate at the
same time with 10 units of force each. What is the
net force acting on the object?
2. What if the boy and the girl pull the heavy crate at
the same time in opposite directions with 10 units
and 5 units of force respectively, what will be the
net force on the object? Will the object move? To
what direction will it move?
3. Suppose another girl pulls the heavy crate in with 5
units of force in the same direction as the girl, what
will be the net force that will act on the object? Will
the object move?
Newton’s Three Laws of Motion
The principles behind Newton’s laws of motion are very significant in
understanding the motion of objects in our universe. Their applications are all around
us. Understanding these laws therefore helps us understand why the things around
us move or behave the way they do.
Newton’s First Law of Motion: Law of Inertia
You learned that if the forces acting on an object at rest are balanced or if
their algebraic sum equate to zero, the object stays at rest. This illustrates Newton’s
10 units
10 units
10 units5 units
10 units5 units
5 units

11
First Law of Motion, a principle that was primarily based on the works of Galileo. The
following examples will help you understand this principle better.
Activity 3
Investigating inertia
Objective:
At the end of this activity, you should be able to demonstrate Newton’s first
law of motion.
Materials:
empty glass 5-peso coins (5 pcs or more)
cardboard plastic ruler
1 peso coin
Procedure
Coin Drop
1. Arrange the setup as shown
in Figure 7.
2. Slowly pull the cardboard
with your hand and observe
what happens.
3. Arrange again the setup as
shown. This time, quickly
flick the cardboard with your
finger. Observe again what happens.
Q9. What happens when you slowly pulled the cardboard? Explain.
Q10. What happens when you flicked the cardboard? Explain.
Stack of Coins
4. Stack the coins on a flat level surface.
5. Quickly hit the coin at the bottom with the edge of the ruler.
Q11. What happens when you hit the coin at the bottom? Why is this so?
Figure 7. Cardboard and coin
Coin
Glass
Cardboard

12
The examples above demonstrate the property of an object to resist any
change in its state of motion. In physics, this property is known as inertia. The coin
dropped into the glass because it was trying to remain in its state of rest. How about
in the second example? How will you explain the behavior of the coins when one of
them was hit with an edge of a ruler?
Measure of Inertia
All objects have the tendency to resist changes in their state of motion or
keep doing what they are doing. However, changing a body’s state of motion
depends on its inertia. A more massive object which has more inertia is more difficult
to move from rest, slow down, speed up, or change its direction.
Newton's first law states that an object at rest will stay at rest or an object
in motion will stay in motion and travel in straight line, as long as no external net
force acts on it. The object will change its state of motion only if there is unbalanced
or net force acting upon it.
Newton’s Second Law of Motion: Law of Acceleration
You learned that when the velocity of a moving body changes, we describe
the motion as one with acceleration. Is there any relationship between acceleration
and any unbalanced force that acts on the body? Find out in the next activity.
Activity 4
Force and acceleration
Objective:
After this activity, you should be able to describe how the net force acting on
an object affects its acceleration.
Law of Inertia
A body will remain at rest or move at constant velocity unless acted
upon by an external net or unbalanced force.

13
Procedure:
Consider this situation below:
A group of students conducted an
experiment to determine the relationship
between the force acting on the object
and its acceleration. They used identical
rubber bands to pull the cart as shown in
Figure 8. They varied the number of
rubber bands to vary the force acting on
the cart. They started with 1 rubber band,
then with 2, 3, and 4 rubber bands, making sure that they stretched the rubber bands
to the same length every time they pull the cart. They used a ticker tape timer to
determine the acceleration of the cart. A ticker tape was connected to the cart such
that when the cart was pulled, the paper tape will be pulled through the timer. And as
the paper tape was pulled through the timer, small dots are formed on the tape.
Starting with the tape for 1 rubber band, they marked the first clear dot and
every 6th
dot thereafter and cut the tape along these points (Figure 9). Then they
pasted the strips side by side in order on a graphing paper to produce the tape chart
for F=1 unit. They did the same for the other tapes to produce tape charts for F=2
units, F=3 units, and F=4 units.
A. Tape chart analysis
1. Obtain from your teacher the copies of the tape charts produced by the
students for the 4 runs.
Q12. Compare the charts. What similarities and differences have you noticed
among them?
The length of strip in each chart represents the total distance travelled by the
cart over a time interval of 0.10 seconds. Recall that the total distance
travelled over a unit time gives the average velocity of the moving body, or
speed when travelling in straight line. Hence, each strip represents the
average velocity of the cart over a time interval of 0.10 seconds.
Figure 8. Cart pulled by rubber bands
Figure 9: Sample tape

14
2. Examine the tape chart for F=1 unit.
Q13. What does the increase in the lengths of the strips suggest? What can you
say about the motion of the cart - is it moving in uniform motion or is it
accelerating? Is this also true with the other runs?
Q14. How do you compare the increase in length of the strips in F= 1 unit? What
does this tell you about the change in the velocity of the cart? Is this also true
with the other tape charts?
Q15. How do you compare the increase in length of the strips among the four tape
charts? Which tape chart shows the greatest increase in the length of the
strips? Which tape chart shows the least increase in the length of the strips?
3. Draw a line that passes through all the dots at the ends of the strips in F=1 unit.
Do the same for the other tape charts.
Q16. Describe the line formed. Does the same pattern exist for the other tape
charts?
B. Quantitative analysis
You can also use the tape chart to compute for the average velocity (vave),
change in velocity (∆v), and acceleration (a) of the cart for each run. Work only
on the tape chart assigned to your group. Other groups will be working on the
other charts. You may follow the simple instruction below.
4. Label each strip 1,2,3,4, and 5 as shown in Figure 10.
5. Compute for the average velocity of the cart over each time interval by
measuring the length of the strip and dividing it by the time covered to travel
such distance. Example, if the length of the strip is equal to 2.5 cm, then the
average velocity during that time interval will be
vave = 2.5 cm / 0.10sec
= 25 cm/s
Figure10: Sample tape chart
1 2 3 4 5

15
Q17. How do the values of vave compare? What does this tell you about the motion
of the cart?
6. Next, determine the difference in the average velocities (∆v) of the cart
between two successive time intervals. Example, you can get the difference in
the average velocities between strips 1 & 2, between strips 2 & 3, and so on.
Q18. How do the computed values of ∆v compare? What does this tell you about
the motion of the cart?
7. Recall that acceleration is defined as the change in velocity per unit of time. To
get the acceleration of the cart, divide your computed values of ∆v in step 6 by
0.10 seconds, the unit of time. Have at least three computed values of
acceleration.
Q19. How do your computed values of acceleration compare?
8. Compute for the average acceleration aave.
9. Ask from the other groups the values of aave for the other tape charts. Record
them all in Table 1 below.
Table 1. Computed values of aave
Tape chart # of rubber bands Computed aave
F = 1 unit 1
F = 2 units 2
F = 3 units 3
F = 4 units 4
Q20. In this activity, the number of rubber bands represents the magnitude or
amount of the force acting on the cart. How is acceleration of the cart related
to the amount of force acting on it?
If the net force acting on an object is constant, its velocity changes at a
constant rate over time. Hence, it is considered to be moving with constant
acceleration. In the tape chart, this is indicated by the uniform increase in length of
the strips over time. But if the force acting on the object is changed, its acceleration
will also change. In your previous activity, you noticed that as the number of rubber
bands increases, the acceleration of the cart also increases. When the net force is
doubled, acceleration is also doubled. When it is tripled, acceleration is also tripled.
We can therefore say that at constant mass, the acceleration of an object is directly
proportional to the magnitude of the unbalanced force F acting on it. This relationship
can be mathematically expressed as:

16
a = kF where k = mass
What if the mass of the object is changed and the force is kept constant?
Acceleration also varies with the mass of the object. As the mass of the object
increases, with the same amount of force applied, its acceleration decreases. This
relationship can also be expressed as:
a = k (1/m) where k = net force
If you combine these two relationships, you would come up with this relationship:
This statement actually pertains to Newton’s second law of motion or Law of
Acceleration, because it is concerned with the relation of acceleration to mass and
force. This can be expressed in equation form as:
Acceleration = Net force / Mass
a = Fnet /m
This is often rearranged as: Fnet = ma
Like any other quantity, force has a unit and is expressed in Newton (N). One
Newton is defined as the amount of force required to give a 1-kg mass an
acceleration of 1 m/s/s, or
1Newton (N) = 1kg/ms2
Sample mathematical problem:
Suppose a ball of mass 0.60 kg is hit with a force of 12 N. Its acceleration will be:
a =
FNet
m
a =
12N
0.60kg
a = 20m / s2
Law of Acceleration
“The acceleration of an object is directly proportional to the magnitude of the
net force acting on it and is inversely proportional to its mass.”

17
If the force is increased to 24 N for the same ball then,
2
40m/s
0.6kg
24N
a  .
Free Fall and Newton’s Second Law of Motion
Suppose you drop two books of different masses from the same height,
which will hit the ground first?
Think about this: If we use the law of acceleration, the heavier book must be
the one to hit the ground first because gravity pulls on it with more force. But if we
use the law of inertia, the lighter book must be the one to hit the ground first because
of its lesser inertia. But if you actually try it out, you would find that they will both
reach the floor at the same time. How come?
Gravity acts on all objects on the earth’s surface and causes them to
accelerate when released. This acceleration, known as the acceleration due to
gravity g, is the same for all objects on earth and is equal to 9.8 m/s2
. This means
that when objects fall, their velocities increase by 9.8 m/s every 1 second.
The books in the example above fall to the ground at the same rate
(acceleration) even if they differ in mass. And since they were released from the
same height at the same time, they will reach the ground at the same time.
Circular Motion and Newton’s Second Law of Motion
Newton’s Second Law was arrived at by studying straight line motion. Does
this law apply to circular motion as well?
Try to whirl an object tied to a string horizontally above your head. Then
observe what happens if you release the object. How does it travel after release?
You learned in Grade 7 that acceleration does not only refer to change in
speed. It also refers to change in direction. In the case of circular motion, the
whirling object accelerates not due to the change in its speed but to the change in
the direction of its velocity. By Newton’s second law of motion, a net force must be
acting on accelerating objects. So where is this net force coming from? For the stone
to move in a horizontal circle, what must you do? You have to pull the stone inward
towards the center of the circular path, right? So the force comes from the string that

18
pulls the object towards the center of its circular path (Figure 11). If you remove this
force by either cutting or releasing the string, you will observe that the object will
continue to move straight and fly off tangential to the path. This is the natural
tendency of the object if there is no net force acting on it, according to the First Law
of Motion. But because of the net force from the string, instead of going straight, the
object accelerates inwards thereby covering a circular path. The object is said to be
in uniform circular motion.
Think about this!
If the object in uniform circular motion is accelerating towards the center of the circle,
why does it maintain a circular path at a constant radius and never get closer to the
center of the circle?
Newton’s Third Law of Motion: Law of Interaction
Activity 5
Action-reaction
Objective:
In this activity, you should be able to compare two interacting forces in terms
of magnitude and direction.
Figure 11. Object in circular motion
F Object flies off
tangentially
Cut or
release
the string
(Circular)
path

19
Materials:
2 spring balances
string
Procedure:
1. Connect 2 spring balances with their hooks. Ask your partner to hold one end
of the balance while you hold the other end horizontally. Pull the spring
balance while your partner just holds the other end. Record the reading on
each balance.
Q21. What is the reading on your balance and that of your partner? What do
these values represent?
Q22. How do you compare the direction of your partner’s and your force?
2. Pull the spring balance harder. Be careful not to exceed the maximum reading
on the spring balance.
Q23. What is the reading on your balance and that of your partner?
Q24. How do you explain your observation?
3. Attach one end of your spring balance to the wall, while the other end is
connected to the second spring balance. Ask your partner to pull the spring
balance. Observe the reading on each balance.
Q25. What is the reading in each balance?
Q26. Compare the direction of the forces exerted on the two ends of the connected
spring balance.
In the simplest sense, a force is a push or a pull. However, Newton realized
that a force is not a thing in itself but part of mutual action, an interaction, between
one thing and another.
For example, consider the interaction between a hammer and a nail. A
hammer exerts a force on the nail and drives it into a board. But this is not the only
force present for there must also be a force exerted on the hammer to stop it in the
process. What exerts this force? The nail does. Newton reasoned that while the
hammer exerts a force on the nail, the nail exerts a force on the hammer. So, in the
interaction between the hammer and the nail, there is a pair of forces, one acting on
the nail and the other acting on the hammer. Such observations led Newton to his
third law: the law of interaction.

20
In Activity 5, you observed the similarities and differences between the
interacting forces in terms of magnitude and direction. This relationship is stated in
Newton’s Third Law of Motion – Law of Interaction.
Because the forces are equal in magnitude and opposite in direction, do you
think they will cancel each other? In this case, no addition of forces will take place
because these forces are acting on different bodies. The spring balances act on
each other.
The difference between the forces related to Law of Interaction and forces in
a balanced state are as follows:
Action-Reaction Forces Balanced Forces
 Two forces are equal in size.
 Two forces are opposite to each
other in terms of direction.
 Two forces have the same line
of action.
 Action acts on one object, while
reaction acts on another object.
 Two forces are equal in size.
 Two forces are opposite to each
other in terms of direction.
 Two forces act along the same
line.
 Two forces act upon the same
object.
References and Links
Herr, N. (2008). The sourcebook for teaching science: Strategies, activities, and
instructional resources, grades 6-12. San Francisco, CA: Jossey-Bass.
Department of Education, Culture and Sports. (DECS). (n.d.). Physics teachers
resource manual. Pasig City. Author.
Department of Education. (DepEd). (2002). Lesson Plans for the 2002 Basic
Education Curriculum: Science IV. Pasig City. Author.
The Physics Classroom (1996-2013). Newton’s laws. Retrieved from
www.physicsclassroom.com
University of the Philippines National Institute for Science and Mathematics
Education Development. (2002). Practical work on high school physics:
Sourcebook for teachers. Quezon City: Author.
Law of Interaction (Action-Reaction)
“For every action, there is an equal and opposite reaction.”

21
WORK AND ENERGY
Overview
In Module 1, you utilized Newton’s Laws to analyze the motion of objects.
You investigated the motion of an object in relation to force, mass and accel eration.
In this module, motion will be investigated from the perspective of work and
energy. The concept of force, which you have taken up in Module 1, will be related to
the concepts of work and energy.
At the end of this module, you should be able to answer the following
questions:
What is Work?
What comes to your mind when you hear the word ‘work’? The word work
has many meanings. When people ask, “What is your work?” They refer to a job or
employment. When people say, “I’ll meet you after work.” They refer to the part of a
day devoted to an occupation or undertaking. When your teacher asks, “Have you
done your homework?” They refer to the task or activity needed to be accomplished.
In Physics, work is an abstract idea related to energy. When work is done it is
accompanied by a change in energy. When work is done by an object it loses energy
and when work is done on an object it gains energy.
In Module 1, you learned that force can change the state of motion of an
object. If an object is at rest, it can be moved by exerting force on it. If an object is
moving, it can be made to move faster or stopped by applying force on it. In order to
say that work is done on an object, there must be force applied to it and the object
moves in the direction of the applied force.
What is work?
What is energy?
How are work, energy and power related?
Unit 1
MODULE
2

22
Work is done if the object you push moves a distance in the direction towards which
you are pushing it.
Figure 1. A girl pushing a chair
No work is done if the force you exert does not make the object move.
Figure 2. A boy pushing a wall
No work is done if the force you exert does not make the object move in the same
direction as the force you exerted.
Figure 3. A waiter carrying a tray
Force, F
displacement, d
direction of motion
no motion
Force, F
Force, F
direction of motion

23
Do activity 1 to see how well you understood ‘work’.
Activity 1
Is there work done?
Objective:
After performing this activity, you should be able to explain if work is done in
situations represented.
Procedure:
Tell whether the situations shown below represent examples of work. Identify the one
doing the work and on which object the work is done. Write in your notebook your
answers and explanations.
2. A man lifting a box to be
placed on a table.
1. A girl pulling her cart.
4. A mango fruit falling from a
branch.
3. A girl carrying a bag walking
down a street.

24
Calculating Work
Work is done when the force (F) applied to the object causes the object to
have a displacement (d) in the same direction as the force applied. The symbol for
work is a capital W. The work done by a force can be calculated as
As you have learned in Chapter 1, the unit of force is
𝑢𝑛𝑖𝑡 𝑜𝑓 𝑓𝑜𝑟𝑐𝑒 = 𝑘𝑔
𝑚
𝑠2
or 𝑛𝑒𝑤𝑡𝑜𝑛, 𝑁
Hence, the unit for Work, W
𝑊 = 𝐹𝑑
𝑢𝑛𝑖𝑡 𝑜𝑓 𝑤𝑜𝑟𝑘 = 𝑢𝑛𝑖𝑡 𝑜𝑓 𝑓𝑜𝑟𝑐𝑒 𝑥 𝑢𝑛𝑖𝑡 𝑜𝑓 𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡
𝑢𝑛𝑖𝑡 𝑜𝑓 𝑤𝑜𝑟𝑘 = 𝑁 𝑚
𝑢𝑛𝑖𝑡 𝑜𝑓 𝑤𝑜𝑟𝑘 = 𝑁𝑚 or 𝑗𝑜𝑢𝑙𝑒𝑠, 𝐽
The unit, joule (J) is named after the English Physicist James Prescott Joule.
This is also a unit of energy. One (1) Joule is equal to the work done or energy
expended in applying a force of one Newton through a distance of one meter.
Sample problem:
Suppose a woman is pushing a grocery cart with a 500 Newton force along the 7
meters aisle, how much work is done in pushing the cart from one end of the aisle to
the other?
𝑊 = 𝐹𝑑
𝑊 = 500 𝑁 (7 𝑚)
𝑊 = 3500 𝑁𝑚
𝑊 = 3500 𝐽
𝑊 = 𝐹𝑑

25
Try solving this:
A book of mass 1 kg is on the floor. If the book is lifted from the floor to the top shelf
which is 2 meters from the floor, how much work is done on the book?
Work is a Method of Transferring Energy
In Grade 7, you learned that there are different ways by which energy can be
transferred from one place to another. Sound and light are transferred by waves;
electrical energy is transferred by moving electrical charges through a complete
circuit; and heat is transferred either by randomly moving particles, or by
electromagnetic waves. Work is also a means of transferring energy from one object
to another.
Do this!
Play a bowling game. Roll a plastic or rubber ball along the floor to hit an
empty plastic bottle.
Figure 4. A ball and a plastic bottle
Is there work done on the ball?
What can a moving ball do?
You have done work on the ball. The force you exerted in pushing the ball is
in the same direction as the motion of the ball. But then you did not continuously
push the ball until it hits the empty bottle. You just gave it a nudge and then it rolled
The force exerted on the ball changed the ball’s motion. ‘Something’ was transferred
to the ball causing it to move continuously. That ‘something’ is called energy. The
energy became energy of motion of the ball.

26
A rolling ball can do work on the plastic bottle. When the ball hits the plastic
bottle, it can push it through a distance. Thus, a moving object can do work on
anything it hits because of its motion energy. Hence, energy is oftentimes defined as
the ability or capacity to do work.
Since work is done on the ball, it gains energy while the person that does
work on it loses energy. In the same manner, the rolling ball that does work on the
empty plastic bottle loses energy while the bottle gains energy. This shows that
when work is done, energy is transferred.
Kinetic Energy
The energy of a moving object is called energy of motion or kinetic energy
(KE). The word kinetic comes from the Greek word kinetikos which means moving.
Kinetic energy quantifies the amount of work the object can do because of its
motion.
The plastic or rubber ball you pushed to hit an empty plastic bottle earlier has
kinetic energy. The force applied caused the ball to accelerate from rest to a certain
velocity, v. In Module 1, you learn that acceleration is the rate of change in velocity.
In the equation,
𝑎 =
𝑣 − 𝑣𝑖
𝑡
where v is the final velocity, vi is the initial velocity and t is the time.
Since the ball started from rest, the initial velocity is zero. Thus, the
acceleration is
𝑎 =
𝑣
𝑡
Substituting this in Newton’s second law
𝐹 = 𝑚𝑎
𝐹 = 𝑚
𝑣
𝑡
The equation in finding the average velocity of the ball is
𝑣̅ =
𝑣𝑖 + 𝑣𝑓
2

27
Since the initial velocity is zero, the average velocity, 𝒗̅ is
𝑣̅ =
𝑣𝑓
2
or
𝑣̅ =
𝑣
2
The distance travelled by the ball before it hits the empty plastic bottle is
given by the equation
𝑑 = 𝑣𝑡̅
where 𝑣̅ refers to the average velocity
𝑑 =
𝑣
2
𝑡
Let’s put the equations together. Since 𝑾 = 𝑭𝒅 and 𝑭 =
𝒎𝒗
𝒕
, we get
𝑊 =
𝑚𝑣
𝑡
𝑑
𝑊 =
𝑚𝑣
𝑡
(
1
2
𝑣𝑡)
𝑊 =
1
2
𝑚𝑣2
This shows that the work done in accelerating an object is equal to the kinetic
energy gained by the object.
𝐾𝐸 =
1
2
𝑚𝑣2
From the equation, you can see that the kinetic energy of an object depends
on its mass and velocity. What will happen to the KE of an object if its mass is
doubled but the velocity remains the same? How about if the velocity is doubled but
the mass remains the same?

28
As you have learned in Module 1, the unit for mass is kg while for velocity it is
meter per second.
Hence, the unit for Kinetic Energy, KE is
𝑢𝑛𝑖𝑡 𝑜𝑓 𝐾𝐸 = 𝑢𝑛𝑖𝑡 𝑜𝑓 𝑚𝑎𝑠𝑠 𝑥 𝑢𝑛𝑖𝑡 𝑜𝑓 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦
𝑢𝑛𝑖𝑡 𝑜𝑓 𝐾𝐸 = 𝑘𝑔 (
𝑚
𝑠
)
2
𝑢𝑛𝑖𝑡 𝑜𝑓 𝐾𝐸 = 𝑘𝑔
𝑚2
𝑠2
But,
𝑘𝑔 ∙
𝑚
𝑠2
= 1 𝑛𝑒𝑤𝑡𝑜𝑛, 𝑁
𝑢𝑛𝑖𝑡 𝑜𝑓 𝐾𝐸 = 𝑁𝑚 𝑜𝑟 𝑗𝑜𝑢𝑙𝑒𝑠, 𝐽
Try solving this:
A 1000 kg car has a velocity of 17 m/s. What is the car’s kinetic energy?
Potential Energy
In activity 1 you were asked if the illustration of a man lifting a box
demonstrates work.
Figure 5. A man lifting a box

29
Which/who is doing work in the illustration? Is it the table, the box, or the
man? Yes you are correct if you answer “The man is doing work on the box.” What is
the direction of the force exerted by the man on the box? Yes, it is upward. What is
the direction of the motion of the box? Yes, it is upward. Then we can say, work is
done by the man on the box.
As discussed previously, work is a way of transferring energy. Since the work
is done by the man, he loses energy. The work is done on the box, hence the box
gains energy.
In Grade 6, you learned about the force of gravity. It is the force that the earth
exerts on all objects on its surface. It is always directed downward or towards the
center of the earth. Hence, when an object is lifted from the ground, the work done is
against the force of gravity. An object gains energy when raised from the ground and
loses energy when made to fall. The energy gained or lost by the object is called
gravitational potential energy or simply potential energy (PE).
For example when a 1.0 kg book is lifted 0.5 m from the table, the force
exerted in lifting the book is equal to its weight.
𝐹 = 𝑊𝑒𝑖𝑔ℎ𝑡 = 𝑚𝑔
The acceleration due to gravity, g is equal to 9.8 meters per second squared.
The work done in lifting the book is
𝑊 = 𝐹𝑑
where the displacement (d) is the height (h) to which the object is lifted.
𝑊 = 𝑚𝑔ℎ
This shows that the work done in lifting an object is equal to the potential
energy gained by the object.
𝑃𝐸 = 𝑚𝑔ℎ
The potential energy of the book lifted at 0.5 m relative to the table is:
𝑃𝐸 = 1 𝑘𝑔 𝑥 9.8
𝑚
𝑠2
𝑥 0.5 𝑚
𝑃𝐸 = 4.9 𝐽

30
If the book is lifted higher than 0.5 m from the table, what would happen to its
potential energy?
The potential energy gained and lost by an object is dependent on the
reference level. Consider a table and a chair shown in Figure 6. If the same 1.0 kg
book is held 1 m above the table, the potential energy gained by it is 9.8 J with the
table as the reference level; it is 14.7 J if the reference level were the chair; and 19.6
J if the reference level were the floor. If the book is released from a height of 2 m, the
potential energy lost when it reaches the level of the table top is 9.8 J; 14.7 J when it
reaches the level of the chair; and 19.6 J when it reaches the floor.
Figure 6. A table and a chair
Try solving this:
If the same 1.0 kg book is lifted to 0.5 m above the table, but the table top is 1.0 m
above the floor, what would be the potential energy of the book if the reference level
were the floor?
The energy of an object above the ground is called potential energy because
it is a ‘stored’ energy. It has the potential to do work once released. Think of water
held in a dam. It has potential energy. Once released, the water has the potential to
move objects along its way. The potential energy of the water is transformed into
kinetic energy.
1 m
0.5 m
table
chair
floor
book
1 m

31
The gravitational potential energy is just one type of potential energy. Another
type is the elastic potential energy. Springs and rubber bands are called elastics.
When elastics are stretched and then let go, they will return to their original form if
they were not stretched beyond their elastic limit.
The force needed to stretch or compress elastics depends on the elasticity of
the object and the change in elongation. The relationship between the force and the
change in elongation (∆𝑙) was first observed by Robert Hooke, hence, the name
Hooke’s Law expressed as:
𝐹 ∝ ∆𝑙
𝐹 = 𝑘∆𝑙
The proportionality holds true as long as the elastic limit of the elastics has
not been reached. The proportionality or force constant k is a measure of the
elasticity of the material.
Consider a spring. Since the force exerted in stretching a spring causes a
change in length, then work is done on the spring. When work is done, energy is
transferred. Thus, the stretched spring gains potential energy. The work done to
stretch the spring a distance x (the symbol x is used instead of d) is equal to its
potential energy. In equation;
𝑊 = 𝑃𝐸 =
1
2
𝑘𝑥2
The elastic potential energy depends on how much the elastic object is
stretched or compressed and the elasticity of the material.
What are the games you play using rubber bands? What do you do with the
rubber bands in the games? Do Activity 2 to see how a rubber band ‘stores’ potential
energy.
Activity 2
Rolling toy
Objective:
After performing this activity, you should be able to explain how a twisted
rubber band can do work and relate the work done to potential energy.

32
Materials Needed:
1 clear plastic container with cover
1 rubber band
1 pc 3-cm round barbecue sticks
1 pc barbecue stick with sharp part cut
masking tape
Procedure:
1. Make a hole at the center of the cover and at the bottom of the plastic
container.
Figure 7. A plastic container with holes
2. Insert the rubber band into the hole at the bottom of the container. Insert in
between the rubber band the 3-cm barbecue stick. Tape the barbecue stick to
keep it in place.
Figure 8. Steps in inserting the 3-cm barbecue stick
3. Insert the other end of the rubber band into the hole in the cover. Insert a bead
or a washer to the rubber band before inserting the long barbecue stick.
Figure 9. Steps in inserting the bead and the long barbecue stick
hole
hole
masking
tape

33
4. You just made a toy. Twist the rubber band by rotating the long barbecue stick.
Figure 10. Rotating the long barbecue stick
5. Lay the toy on the floor. Observe it.
Figure 11. Finished toy
Q1. What happens to the toy?
Q2. What kind of energy is ‘stored’ in the rubber band?
Q3. What kind of energy does a rolling toy have?
Q4. What transformation of energy happens in a rolling toy?
Work, Energy, and Power
So far, we have discussed the relationship between work and energy. Work is
a way of transferring energy. Energy is the capacity to do work. When work is done
by an object it loses energy and when work is done on an object it gains energy.
Another concept related to work and energy is power.
Power is the rate of doing work or the rate of using energy. In equation,
𝑃 =
𝑊𝑜𝑟𝑘
𝑡𝑖𝑚𝑒
=
𝐸𝑛𝑒𝑟𝑔𝑦
𝑡𝑖𝑚𝑒

34
The unit for power is joules per second. But maybe, you are more familiar
with watts which is commonly used to measure power consumption of electrical
devices. The unit watt is named after James Watt who was a Scottish inventor and
mechanical engineer known for his improvements on steam engine technology. The
conversion of unit from joules per second to watts is:
1 𝑤𝑎𝑡𝑡 =
1 𝑗𝑜𝑢𝑙𝑒
1 𝑠𝑒𝑐𝑜𝑛𝑑
Do Activity 3 to see your power output in walking or running up a flight of
stairs.
Activity 3
How POWER-ful am I?
Objective:
After performing this activity, you should be able to compute for your power
output in walking or running up a flight of stairs.
Materials Needed:
meterstick
timer
Procedure:
1. Write the group members’ names in the first column of Table 1.
2. Enter each member’s weight in column 2. To solve for the weight, multiply the
mass (in kg) by acceleration due to gravity (g=9.8 m/s2
).
3. Measure the height of the flight of stairs that you will climb. Record it on the table.
h

35
4. Each member will walk or run up the flight of stairs. Use a stopwatch or any
watch to get the time it takes for each member to climb the stairs. Record the
time in the 4th
column.
5. Solve for the energy expended by each member. Record them in the 5th
column
of the table.
6. Compute for the power output of each member.
Table 1
Name Weight (N)
Height of
stairs (m)
Time taken to climb
the stairs (s)
Energy
expended
(J)
Power
(J/s)
Q1. Who among the group members had the highest power output?
Q2. What is the highest power output?
Q3. Who among the group members had the lowest power output?
Q4. What is the lowest power output?
Q5. What can you say about the work done by each member of the group? Did each
member perform the same amount of work in climbing the stairs?
Q6. What factor/s determined the highest/lowest power output?
These are the concepts that you need to remember about work and energy:
 Work is done on an object when the force applied to it covers a distance in
the direction of the applied force.
 Work is a way of transferring energy.
 When work is done by an object it loses energy and when work is done on an
object it gains energy.
 The energy of an object enables it to do work.

36
 A moving object has energy called energy of motion or kinetic energy.
 An object above a specified level has energy due to its position called
potential energy.
 An elastic object that is stretched or compressed or twisted has energy called
potential energy.
 Power is the rate of doing work or the rate of using energy.
Henderson, Tom. (2013). Work and energy. Retrieved from
https://itunes.apple.com/us/book/work-and-energy/id611940649?mt=13
Hewitt, P.G. (2002). Conceptual physics. USA: Prentice-Hall, Inc. Saddle River, New
Jersey.
Kirkpatrick, L.D., & Wheeler, G.F. (1998). Physics: A world view. Forth Worth:
Saunders College.
Ostdiek, V.J., & Bord, D.J. (1987). Inquiry into physics. New York: West Publishing.
DepEd. Science and Technology IV. SEDP Series. (1992). Philippines: Book Media
Press, Inc.

37
HEAT AND TEMPERATURE
Overview
Heat transfer happens around us all the time. Although we do not see how
this process actually takes place, its effects are evident. In fact, we rely on these
effects everyday in many of the activities that we do. Understanding the concepts
behind heat transfer therefore helps us do our activities more efficiently.
You have learned in previous grades that heat transfer takes place between
objects or places of different temperatures, and that heat transfers from an object of
higher temperature to an object of lower temperature. You have also learned that
heat can be transferred through conduction, convection, or radiation, and that heat
transfers either through moving particles or electromagnetic waves. Lastly, you also
learned about some factors that affect heat transfer, like the conductivity of the
materials.
This time, you will learn more about heat transfer by exploring its effects on
materials. You will also learn about the factors that affect the amount of heat that an
object can absorb or release and describe how these are related to the amount of
heat transferred.
People often interchange the use of the terms heat and temperature in their
daily conversation. They also think that heat and temperature are just the same. But
for physicists, heat and temperature are two different concepts. So in this module,
you will also learn the difference between heat and temperature.
At the end of this module, you are expected to answer the following key
questions:
Unit 1
MODULE
3

38
Points to remember…
Remember that heat is the transfer of energy between objects or places
because of difference in temperature. Heat exists as ‘energy in transit’ and it is not
contained in an object. The energy that is actually contained in an object due to the
motion of its particles is called thermal energy. The thermal energy of an object is
changed if heat is transferred to or from it. Since the amount of heat transferred
relates to the amount of change in thermal energy, the term heat in this module is
also used to refer to the measure of thermal energy transferred.
Note also that the activities in this module involve hot and boiling water, so
extra care should always be observed.
Activity 1
Explaining hotness or coldness
This first activity deals with one of the major effects of heat transfer, which is
temperature change. You will describe the hotness or coldness of an object in terms
of its temperature. You will also compare the changes in the temperature of water to
determine the relationship between the amount of heat transferred and the resulting
temperature change.
Materials Needed:
3 identical containers
thermometer
hot water
tap water (room temperature)
cold water
What happens to solids, liquids, or gases when they absorb or
release heat?
Does heat affect all kinds of materials in the same way?
Are heat and temperature one and the same?

39
Procedure:
1. Half-fill the three containers with equal amount of cold water. Arrange them
next to one another as shown in Figure 1 below.
2. Place your finger for a while into any of the containers.
Try to recall your lesson on Heat Transfer in Grade 7 and answer the following
questions:
Q1. What actually transferred when you dipped your finger into the water? In what
direction did it transfer?
Q2. Was the water ‘hot’ or ‘cold’? Explain.
Discuss your answers with the group. Try to estimate the temperature of the
water in the containers.
3. Measure with a thermometer the temperature of the water in each container.
Record your measurements in Table 1 below. (Note: The initial temperature of
the water in each container should be the same as they come from the same
source.)
Figure 1
1 2 3

40
Table 1: Data for Activity 1
Estimated temperature of water: ____ (°C)
Container
Measured
temperature (°C) Change in
temperature
Initial Final
Container 1
Container 2
Container 3
Q3. How close is your estimated value to the measured temperature of the water?
4. Add the same amount of hot water to container 1, tap water to container 2 and
the same cold water to container 3. Leave the containers for a while.
5. Dip your fingers again, this time into the three containers. Make sure that you
do not dip the same finger into the containers.
Q4. Which container feels ‘hottest’? Which container feels ‘coolest’?
Q5. What do you think causes the difference in the hotness or coldness of the
water inside the containers?
6. Measure and record the temperature of the water in all containers. Calculate
the change in the temperature of water in each container.
Q6. In which container(s) is heat transfer taking place? What evidence best
supports your answer? Within this container, which absorbs heat? Which gives
off heat?
Q7. In which container was there the greatest amount of heat transferred? What is
the basis of your answer?
Q8. How are the amount of heat transferred and the change in temperature of
water related?
___________________________________________________________________
You have just observed that if heat is absorbed or given off by an object, its
temperature changes. If the object absorbs heat its temperature rises. How do we
explain the rise in temperature when heat is absorbed? In this next activity, you will
take a closer look at what is actually happening at the particle level and infer what
happens to the particles of an object when heat is added to it.

41
Activity 2
Dye in water
At the end of this activity, you should be able to explain the scattering of the dye
in water at different temperatures.
Materials Needed:
3 transparent containers
1 thermometer
3 plastic droppers
hot water
tap water (room temperature)
cold water
dye (Food color)
Procedure:
1. Fill the three containers separately with cold water, tap water, and hot water.
2. Measure the temperature of the water in each container. Record your
measurements in Table 2 below.
Table 2: Data for Activity 2
Container
Temperature
(0
C)
Observations
Container 1
Container 2
Container 3
3. With the dropper, place a drop of dye into the center of each container as
shown in Figure 2. (Note: It is better if you place drops of dye into the three
samples simultaneously.)

42
4. Carefully observe and compare the behavior of the dye in the three containers.
Write down your observations in Table 2.
Q9. What similarities and differences did you observe when a drop of dye was
added to each container?
Q10. In which container did the dye scatter the fastest? In which di it scatter the
slowest?
Q11. How do you relate the temperature of the water to the rate of scattering of the
dye?
_________________________________________________________________
You learned in Module 2 that moving objects possess kinetic energy. All the
objects that you see around you that are moving possess kinetic energy. But do you
know that even the very small things that you cannot see, like the particles of
objects, are also moving and have kinetic energy? Take for example the water inside
the containers in Activity 2. The scattering of the dye through the water indicates that
the particles of water are moving. You will learn more about the movement of the
particles of matter in the third quarter when you discuss about the Particle Theory of
Matter.
You also noticed that the rate of scattering of the dye throughout the water
differs in each container. It can then be inferred that the speed of the particles of
water varies in each container. Since kinetic energy depends on speed, the kinetic
energies of the particles also vary.
Q12. In which container are the particles of water moving fastest? In which
container are the particles moving slowest?
Q13. How is temperature related to the speed of the particles?
Figure 2

43
Q14. How is temperature related to the kinetic energy of particles?
If heat is added to an object, the particles of the object gain kinetic energy
and they move faster. Since temperature is directly related to kinetic energy, any
gain in kinetic energy would cause the temperature to increase. Conversely, if heat is
transferred or removed from an object, it loses kinetic energy, its particles move
slower and the body’s temperature decreases.
Thermal Expansion, the Working Principle of the Mercury
Thermometer
You know that temperature is measured by the use of thermometer. You
have most probably used this device many times. The thermometer commonly
available in our schools is the liquid thermometer, which has a column of either
mercury or alcohol. When the thermometer is placed in contact with any object the
mercury column either rises or drops.
Now, why does the liquid inside the tube of the thermometer go up or down?
This happens because the mercury inside the tube expands or contracts in response
to a change in temperature. When the thermometer bulb is placed in hot water, the
liquid inside the tube expands. As it does, it takes more space and so it goes up the
tube. When the bulb is placed in cold water, the liquid contracts and so it goes down
the tube.
In physics, this is called thermal expansion, another effect of heat transfer.
But thermal expansion does not apply only to the liquid inside the thermometer. In
fact, it applies to almost everything around us, be it a solid, a liquid, or a gas. If
allowed by your teacher, you may try this simple activity to demonstrate expansion of
a solid when heated.
Figure 3. Thermometers in a) hot
and b) cold liquid

44
Try this!
You will need: copper wire (around 2m long), candles, meterstick, 2 iron stands with
clamps or rings, standard weight (or any mass around 500g)
What to do:
Prepare the setup as shown below. Make sure that the ends of the copper
wire are tied or clamped firmly. Hang the weight in the middle of the wire. Use
the candles to warm the wire at different points. Do this for 1 or 2 minutes and
observe what will happen to the height of the weight.
If you tried out this experiment, you would have observed that when you
heated the entire length of the wire, the weight moved down or its height decreased
a little. This indicates that the wire expanded or increased in length when heated.
There are so many applications of thermal expansion around us. Some are
beneficial to us; others can also be a burden to us. One example of thermal
expansion in solid is the sagging of electrical power lines or telephone wires on hot
days. This happens because heat causes them to expand. Have you ever wondered
why it is difficult to open a jar that was just taken out of the refrigerator or why
motorists are advised not to overinflate their car tires or fill their gasoline tanks to the
brim? How will you apply the concepts of thermal expansion to explain all these?
WeightCopper wire
Ruler or
meterstick
Figure 4. Setup for expansion of wire experiment

45
Phase Change
Another change that may occur when heat is added to or taken out from an
object is phase change. For example, you know that water can change from solid
(ice) to liquid (water) or from liquid to gas (steam). The next activity will allow you to
observe the changes that take place when ice turns to liquid water.
Activity 3.1
What happens when ice melts?
After this activity, you should be able to answer this question:
What happens to the temperature of water while changing from
ice to liquid water?
Materials needed:
crushed ice
1 glass container
timer (stopwatch)
stirring rod
Procedure:
1. Put some crushed ice and a little cold water into the container.
2. Stir the contents of the container for few seconds; then, measure the
temperature of the contents.
Avoid letting the thermometer touch the bottom of the container to ensure that
you are actually measuring the temperature of the water.

46
Record your temperature reading in Table 3 below.
Table 3: Temperature readings for melting ice
3. Repeat step 2 every 2 minutes. Make sure that you stir and measure exactly
the same way each time. Record each measurement in Table 3.
Q15. Why does the ice inside the container melt after sometime?
4. Continue measuring until the ice has totally melted and even after it has
already melted completely (around 4-6 minutes more).
5. Construct a temperature against time graph. Draw a smooth line that passes
through almost all the points.
Q16. Which is your dependent variable? Which is your independent variable?
(Note that the independent quantity is plotted along the X-axis while the
dependent quantity is plotted along the Y-axis.
Q17. Describe your graph.
Q18. Describe the temperature of the water while the ice melting.
Q19. Describe the temperature of the water after the ice has melted.
Were you able to see in your graph a horizontal line similar to the part
encircled in Figure 5? This was during the time when solid (ice) was turning to liquid
water. During this stage, the temperature of the water remained the same, as shown
by the horizontal line. Remember that a change in temperature indicates a change in
kinetic energy. In this case, there was no change in the kinetic energy of the
particles. So what happened to the heat energy that was continuously transferred to
the water? The energy absorbed by the water is used by the particles to overcome
Time (min) Temperature (°C)
0 (Initial)
2
4
6
8
10
12
14

47
the attractive forces between them, and not to increase the speed of particles. The
temperature of the water will only start to increase after the ice has totally melted.
What if you continue to heat the water further until it boils? What do you think
will happen to the temperature of the water?
Activity 3.2
What happens to the temperature of water as it
boils?
Materials:
beaker
stirrer
thermometer (can measure up to 100°C)
alcohol burner
water (hot water)
stand or tripod with wire gauze
Procedure:
1. Fill the beaker with 100 mL hot water and place it above the alcohol burner
using the tripod with wire gauze.
2. Measure and record the temperature of the water every 2 minutes until it
boils. Once the water starts to boil, continue taking the temperature for 4-6
more minutes.
3. Plot the graph of temperature against time.
Q20. Describe and interpret your graph.
Q21. What similarities and differences have you noticed between your graphs in
Activity 3.1 and Activity 3.2?
If you heat up the same sample from ice to water then from water to gas
(vapor) and plot the graph of temperature vs time, it would look like the graph in
Figure 5. The graph shows that the ice absorbs heat as evidenced by the
temperature rise; the temperature remains the same when ice starts to melt and until
all the ice has melted; then the temperature rises again until water boils. The
temperature remains constant at boiling temperature when water starts turning to
steam and until all the liquid water has become water vapor.

48
In Activity 1, you found that the high temperature water transferred more heat
than water at a lower temperature. This is shown by a greater increase in
temperature of the object that absorbed the heat. What other factors determine the
amount of heat that a body can transfer?
Activity 4
What is the relationship between the mass of a
material and the amount of heat it can transfer?
Task:
In this activity, your group is assigned to plan and conduct a simple investigation
to determine the relationship between the mass of a material and the amount of
heat that it can transfer. You need to gather and analyze data to come up with
answers to the question given above. Apply what you learned in grade 7 about
doing simple investigations.
1. Start with your group’s prediction below:
Prediction: ____________________________________________________
_____________________________________________________________
_____________________________________________________________
Figure 5. Phase change of water
as heat is added
Melting
Vaporization
Temperature
Time
Heat
100°C
(Boiling point)
0°C
(Melting point)
Ice
Water
Steam
(vapor)

49
2. Below are some guides to help you with your task.
a. What are your variables?
Independent variable:
Dependent variable:
Controlled variable (constant):
b. What materials are you going to use for your simple investigation?
c. What quantities are you going to measure for your data?
d. How are you going to analyze and present your quantities (data) to
describe the relationship among the variables?
3. Write your step-by-step procedure. Let your teacher check your procedure first
before you proceed. Precautions should always be observed.
4. Present your data systematically.
If you were successful in your investigation, you would have realized that the
amount of heat transferred depends not only on the temperature of the material. It
also depends on the mass or amount of material. Objects with greater mass have
more thermal energy and can transfer more heat.
___________________________________________________________________
Heat Capacity
Earlier in this module, you learned that materials expand when heated or
contract when cooled. This time, you will study another thermal property of materials
—their ability to absorb or release heat that results in temperature change. In
science, the amount of heat needed by a material to increase its temperature by a
degree is called heat capacity (C). To be more specific, the term specific heat
capacity (c) is used, and this refers to the amount of heat required to increase the
temperature of one unit mass of a given material by one Celsius degree. For
example, water has a specific heat capacity of 1 cal/g°C. So it takes 1 calorie of heat
to raise the temperature of 1 gram of water by 1°C.

50
Activity 5
Comparing heat capacities
Objectives:
After performing this activity, you should be able to compare the heat
capacities of the given liquid samples.
Materials:
2 identical small containers (each with 100mL of liquid sample)
2 identical large containers (large enough to accommodate the small
containers)
2 thermometers
hot water
liquid samples: water, cooking oil
Note: Store the liquid samples in the same room to ensure that both are at
room temperature when you do the activity.
Procedure:
1. Pour 100mL of water into one of the small containers and the same amount
of cooking oil into the other container. Measure and record their initial
temperature in Table 4 below.
Table 4
Initial
temperature (C)
Heating time
(sec)
Cooking Oil
Water
2. Place the small container with oil in a larger container with hot water. Make
sure that the hot water does not mix with the liquid sample.
3. Measure the time it takes for the oil to increase in temperature by 5 °C.
Example, if the initial temperature of the liquid is 28C, take the time it takes
for the temperature to reach 33C. Record your measured heating time in
Table 4.

51
4. Do the same with the water sample. Make sure that the amount and
temperature of the hot water is the same for both samples. Record also your
measurement in Table 4.
Q22. Which liquid requires more time to increase in temperature by 5 degrees?
Q23. Which liquid requires more heat to increase in temperature by 5 degrees?
Q24. Which liquid has a greater heat capacity?
Different materials have different specific heat capacities. Many metals have
low specific heat capacities. This makes them easy to heat up and cool down. Water,
on the other hand, has a high specific heat capacity and so it takes a long time to
heat and a long time to cool. This makes the water a good coolant for car radiators.
Because of its high specific heat capacity, it can absorb a large amount of heat
without causing its temperature to rise too high.
Heat and Temperature
So far, you have already recognized the relationship between heat and
temperature. So how do they differ? Go back to your previous experiments and
analyze your findings. Then try to answer questions below.
 Which has a higher temperature, 1 cup of boiling water or 1 teapot of
boiling water? Which can transfer more heat, 1 cup of boiling water or 1
teapot of boiling water? Explain your answer.
 Which can transfer more heat, a cup of boiling water or a cup of tap
water? If you increase the amount of the boiling water and tap water
twice, will their temperature change? Explain your answer.
 Which can transfer more heat, a cup of boiling water or 1 basin of tap
water? (You may try this out if you have time.)
So how are heat and temperature different? Well, here are the important
points to consider about the difference between heat and temperature. First, heat is
a form of energy while temperature is not a form of energy. Temperature is a
measure of the average kinetic energy of the particles and it does not depend on the
mass of the object. It can be measured directly with the use of thermometers. Heat
cannot be measured directly. But you can make use of the measurable quantities
related to heat to determine how much heat (Q) is absorbed by the object. These are
the change in temperature (∆T), mass (m), and specific heat capacity (c) of the
object. The relation among these quantities is expressed as: TcQ  m .

52
Links
Chalfant, H., Peyron, M., Rachke, C. (2005, Fall). Heat and temperature. Sci Ed,
491. Retrieved from
http://www.biol.wwu.edu/donovan/SciEd491/HeatTempUnit.pdf
Expansion and contraction. (n.d.). Retrieved from
http://schools.cbe.ab.ca/b682/pdfs/Science%207/Heat-and-Temperature-
Unit3_T4_T6.pdf

53
ELECTRICITY
Overview
Electricity is a part of our daily lives. Many of the activities we do everyday
depend on electricity. The discovery of electricity changed people’s lives. Can you
watch your favorite show on TV without electricity? Can you use your computers
without electricity? Imagine our life today without electricity.
You have been learning a lot about electricity from Grade 3 to Grade 7. You
have learned about its sources and uses; what materials make good conductors of
electricity; what makes up an electric circuit; and how electrical energy is transferred
or transformed into other forms of energy.
In this module, you will learn more about electricity. There are three quantities
that you should be familiar with in the study of electricity. These are electric current,
voltage, and resistance. You will use the relationships among these quantities in
learning about circuit connections. You will also learn that some of the safety
precautions you have been warned about can be explained by the relationships
among voltage, current, and resistance.
At the end of this module you should be able to answer the following
questions:
How do voltage and resistance affect electric current?
What are the safety precautions needed in using electricity?
Unit 1
MODULE
4

54
Electric Current
In Grade 7, you learned that a circuit is any arrangement of a source of
energy (battery), connecting wires, and a load (e.g. bulbs). You also learned that a
complete or a closed circuit provides a path for electrical charges to flow. Electric
current is a measure of the number of electrical charges passing through a cross-
section of a conductor in a given time. The direction of conventional current or simply
current is from the positive terminal of the battery to the negative terminal.
The symbol for current is capital letter I. The unit, ampere (A), is named after
Andre-Marie Ampere, a French physicist who made important contributions to the
theory of electricity and magnetism.
An ammeter measures electric current. Figure 1 shows how the ammeter is
connected in a circuit. The positive terminal of an ammeter is connected to the
positive terminal of the energy source (e.g. battery) while the negative terminal is
connected to the negative terminal of the energy source as shown in Figure 1.
Figure 1. Ammeter connected in a circuit
Voltage
What makes the charges move in a closed circuit? In Module 2, you learned
that when work is done on an object, energy is transferred which can become energy
of motion of the object. In a circuit, work must be done on the charges to make them
move. The battery supplies the energy in electric circuits. The chemical energy in the
battery is transformed to electrical energy. This electrical energy moves the charges
in a circuit.
A battery consists of several dry cells or wet cells. Both dry and wet cells
contain a conducting medium called electrolyte. The batteries we use in flashlights
and watches are dry cells.

55
The symbol for voltage is capital letter V. The unit, volts (V), is named after
the Italian physicist Alessandro Volta who invented the voltaic pile, the forerunner of
what we now call the dry cell.
A voltmeter measures voltage. Figure 2 shows how the voltmeter is
connected in a circuit. The voltmeter should be connected across the load being
tested. The positive terminal of a voltmeter is connected to the positive terminal of
the bulb while the negative terminal is connected to the negative terminal of the bulb
as shown in Figure 2.
Figure 2. Voltmeter connected across the load
If voltage is needed for charges to flow, how does the amount of voltage affect
current? Find out in Activity 1.
Activity 1
Current and voltage
Objectives:
1. measure the electric current and voltage in a circuit using an ammeter
and voltmeter respectively; and
2. determine the relationship between electric current and voltage.
positive terminal
of the bulb
negative terminal
of the bulb

56
Materials Needed:
1 ammeter 1 voltmeter
2 dry cells (1.5 V each) 2 dry cell holders
4 connecting wires 1 switch
1 bulb 1 bulb holder
Procedure:
1. Construct a simple circuit using a dry cell, a bulb, a switch and an ammeter.
Close the circuit by turning on the switch. Observe the bulb and the ammeter.
Record the ammeter reading in Table 1. Upon completion of the task, switch off
the circuit.
Figure 3. Ammeter connected in a circuit with one dry cell
Q1. What is the reading on the ammeter?
2. Add another dry cell to the circuit. Record the electric current measurement in
Table 1. Once the task is done, turn off the switch.
Figure 4. Ammeter connected in a circuit with two dry cells
switch
battery
bulb
ammeter

57
Table 1
No. of batteries Voltage (V) Current (A)
1
2
Q2. Compare the brightness of the bulb with one dry cell to its brightness when
there are two dry cells in the circuit.
Q3. What is the ammeter reading this time?
Q4. What can be inferred about the current passing through the bulb?
3. Connect the voltmeter in the circuit as shown in Figure 5. Switch on and record
the voltage in Table 1. Once the task is done, turn off the switch.
Figure 5. Voltmeter connected in a circuit with one dry cell
Q5. What is the voltmeter reading?
4. Add another dry cell to the circuit. Record the voltmeter reading in Table 1.
Observe the brightness of the bulb. Once the task is done, turn off the switch.
Figure 6. Voltmeter connected in a circuit with two dry cells

58
Q6. Describe the brightness of the bulb.
Q7. What is the voltmeter reading this time?
Q8. What can be inferred about the voltage across the bulb?
Q9. Refer to Table 1, how are voltage and current related?
In Activity 1, the current and voltage in circuits with 1 dry cell and 2 dry cells
were compared. You observed that the ammeter and voltmeter readings are greater
in the circuit with 2 dry cells as compared to the circuit which has only one dry cell.
Also, the bulb in the circuit with 2 dry cells glowed brighter than the bulb in the circuit
with only 1 dry cell. The activity showed that as the voltage increases, the current
also increases.
However, a circuit is not only about voltage and current. There is another
component which is the load. A load is any component in a circuit that converts
electricity into light, heat, or mechanical motion. In the circuit you constructed in
Activity 1, the bulb is the load. If two bulbs were used in the circuit, would there be a
change in the circuit current? You will find out in Activity 2.
Resistance
When electric charges flow through the wires and loads of the circuits they
encounter resistance or a hindrance to their movement. So another factor that affects
the flow of charges or current is resistance.
The symbol for resistance is capital letter R. The unit, ohms (Ω) is named
after the German physicist Georg Simon Ohm.
How is current affected by the resistance of the load in a circuit? Do activity 2
to find out.
Activity 2
Current and resistance
Objectives:
After performing this activity, you should be able to determine the
relationship between electric current and resistance.

59
Materials Needed:
1 ammeter 2 dry cells
2 dry cell holders 4 connecting wires
1 switch 3 flashlight bulbs (voltage rating of 2.5V each)
3 bulb holders
Procedure:
1. Construct a simple circuit using one bulb, 2 dry cells and an ammeter as shown
in Figure 7. Record the electric current measurement in Table 2. Once the task
is done, turn off the switch.
Figure 7. Ammeter connected in a circuit with one bulb and two dry cells
2. To increase the resistance, add another bulb in the circuit. Connect the
ammeter and record the electric current measurement in Table 2. Once the
task is done, turn off the switch.
Figure 8. Ammeter connected in a circuit with two bulbs and two dry cells

60
3. To further increase the resistance, add another bulb in the circuit. Connect the
ammeter and record the electric current measurement in Table 2. Once the
task is done, turn off the switch.
Figure 9. An ammeter connected in a circuit with three bulbs and two dry cells
Table 2
Q10. Based on Table 2, what happens to the current in the circuit as the resistance
increases (increasing of bulbs)?
4. Connect the ammeter at different points around the circuit shown in Figure 10.
Make sure that the positive terminal of the ammeter is connected to the positive
terminal of the dry cell while the negative terminal is connected to the negative
terminal of the dry cell. Once the task is done, turn off the switch.
Figure 10. Ammeter connected between two bulbs in a circuit
No. of bulbs Current (A)
1
2
3
A
B C

61
Q11. Compare the current at different points in the circuit.
Q12. What can you infer about the current through the circuit?
In Activity 2, you added bulbs to the circuit to see if the current in the circuit
will be affected. You observed that keeping the number of dry cells the same, adding
more bulbs resulted in a decrease in current. Since adding more bulbs means
increasing the resistance in the circuit, it can be inferred that the resistance limits the
current in the circuit. You further observed that the current is the same in any part of
the circuit as evidenced by the ammeter readings.
How is the result in Activity 1, related to the result in Activity 2? The results of
Activity 1 showed that for a fixed resistance (one bulb), as the voltage increases, the
current also increases. For Activity 2, the results showed that keeping the voltage the
same (2 dry cells), when the resistance increases, the current decreases.
At this point, you are already very familiar in constructing a circuit. In Activity
3 you will find out if connecting loads in different ways would affect the current and
voltage of the circuit
Activity 3
What’s the connection?
Objectives:
1. connect loads in different ways and
2. explain the similarities and differences between the circuit connections.
Materials Needed:
For Circuit A:
3 connecting wires
2 identical bulbs with holder
2 dry cells with holder
For Circuit B:
4 connecting wires
2 identical bulbs with holder
2 dry cells with holder
voltmeter for both circuits

62
Procedure:
1. Construct a circuit using three connecting wires, two identical bulbs and two
batteries such that when one bulb is unscrewed the other bulb goes out also.
Once you’re done with the task, disconnect the battery from the circuit.
2. Draw your setup. Label this Circuit A.
3. Trace the paths of current in Circuit A.
Q13. How many path/s of current are there in the circuit?
Q14. Why did the other bulb go out also when you unscrewed the other?
4. This time, construct a circuit using four connecting wires, two identical bulbs
and two batteries such that when one bulb is unscrewed, the other bulb
remains lighted. Once you’re done with the task, disconnect the battery from
the circuit.
5. Draw your setup. Label this Circuit B.
6. Trace the path of current in Circuit B.
Q15. How many paths can the current take in Circuit B?
Q16. Explain why the other bulb remains lighted when you unscrewed one of them.
7. Put Circuits A and B side by side. Observe the brightness of the bulbs.
Q17. Which circuit has brighter bulbs, A or B?
Q18. Based on the brightness of the bulbs, compare the current in Circuit A and
in Circuit B?
8. Measure the voltage across the two bulbs as well as the voltage across each
bulb in Circuit A. Record your readings in Table 3. Do the same in Circuit B.
Table 3
Circuit Voltage drop (V) Voltage across the two
bulbs (V)Bulb 1 Bulb 2
A
B
In Circuit A, the bulbs are connected in series, while in Circuit B, the bulbs
are connected in parallel. Series and parallel connections are the two ways of wiring
loads. In a series connection, there is only one path for the current. In a parallel
connection the current from the battery can branch out to the two bulbs. Hence the
current can take the path through Bulb 1 and the path through Bulb 2.

63
The current in Circuit A takes only one path, passing through the two bulbs.
When one bulb is unscrewed or removed, a gap is created. A gap or a break
anywhere in the path stops the flow of charges and therefore no current passes
through to the other bulb.
In Circuit B, the current can take two paths - one path for each bulb. When
one bulb is unscrewed or removed, the other bulb is still part of a complete circuit
and remains lighted.
Let us compare the other characteristics of Circuits A and B. Circuit A is
similar to the circuit of three bulbs you made in Activity 2. The bulbs are connected in
series. In this type of connection, the resistance increases with the number of bulbs
added in the circuit. The total resistance in the circuit is the sum of the resistance
offered by each bulb.
You observed in Activity 2 that as the total resistance increases, the current
through the circuit decreases. You also measured the current and voltage at different
parts of the circuit. Your measurements showed that the current is the same
anywhere in a series circuit, and the sum of the voltages across each bulb equaled
that of the voltage source.
On the other hand, Circuit B has 2 bulbs which are connected in parallel.
You observed that the voltage across each bulb is almost equal to the voltage of the
two dry cells, indicating that the voltage anywhere in the circuit is the same.
However, when the brightness of the bulbs in Circuit B is compared to that of the
bulbs in Circuit A, those of Circuit B were brighter than those of A. This means the
current in B is greater than the current in A. Since the voltage in A and B are the
same (2 dry cells), the greater current in B indicates that the total resistance of
Circuit B is less than the total resistance of Circuit A. We can infer that when loads
(bulbs) are connected in parallel, the total resistance of the circuit decreases; when
the loads are connected in series, the total resistance increases. Table 4 compares
the total current, total voltage and total resistance of series and parallel circuits.
Table 4
Series connection Parallel connection
Total current Same as current in individual load Equal to the sum of current in
individual loads
Total voltage Equal to the sum of the voltages
across each load
Same anywhere across two
points in the circuit
Total
resistance
Increases with increasing load Decreases with increasing load
Look at the connections of wirings in your house. Which are connected in
series? Which are connected in parallel? What are the advantages and
disadvantages of each type of connection?

64
Safety in Using Electricity
Your parents have probably cautioned you about the use of electrical devices
even before you reached school age. You were told not to touch electrical outlets or
insert anything into it. You were told not to touch any electrical wires in the house.
Well they may not have explained it to you back then, but they have valid reasons.
Firemen advise homeowners to check the electrical connections in their
homes especially the condition of the wires. They advise homeowners to replace
exposed electrical wires. Why is there a need to cover exposed wires? You will find
the answer in Activity 4.
Activity 4
Stay safe!
Objectives:
1. describe the heating effect of current;
2. explain what a short circuit is; and
3. explain the reason behind some safety practices in the use of electricity.
Materials Needed:
For Activity 4A For Activity 4B
2 dry cells in a battery holder 2 connecting wires
2 connecting wires 2 dry cells in a battery holder
1 fine strand of copper wire (20 cm long) 1 bulb in a bulb holder
2 small blocks of wood
4 thumbtacks
2 short candles
Timer
Procedure:
4A. What makes it hot?
1. Place two wooden blocks side by side. To keep them from being moved, place
masking tape underneath each block to keep them steady on the table.
2. Place two thumbtacks on each wooden block near the space between them.
Wrap the copper wire tightly around the thumbtacks as shown, leaving two free

65
ends on the same wooden block. Press the thumbtacks fully until the head of
the thumbtacks is just above the wood.
Figure 11. Copper wire wrapped around the thumbtacks
3. Place a candle on top of the wires as shown below.
Figure 12. A candle on top of the copper wires
4. Connect the two free ends of the copper wire to the battery using the
connecting wires. Leave the circuit closed for 30 seconds and then disconnect
the battery. Observe the candle. Write your observation and explanation.
Figure 13. A circuit with copper wires connected to two dry cells
5. Try adding another dry cell as shown in the circuit using another candle.
Repeat steps 3 and 4 and write your observation.
Thin copper wire
Candle
Free
ends

66
Figure 14. A circuit with copper wires connected to three dry cells
Q19. What happened to the candle for both setups?
Q20. When you increase the voltage by adding another dry cell, what happens to
the amount of current in the circuit?
Q21. Compare the effect on the candle with two dry cells and with three dry cells
in the circuit. What is produced in the wires that affected the candle? How
does the effect on the candle relate to the amount of current in the wire?
4B. Don’t keep it short!
1. Remove about 2 cm insulation from the ends of the connecting wires.
2. Construct a circuit using the bulb, 2 batteries, and connecting wires with
exposed parts you made in step 1.
Figure 15. A circuit with exposed wires

67
3. Make the exposed parts of the wire touch momentarily. Do not keep them in
contact for so long.
Q22. What happened to the bulb?
4. Draw the setup and trace the path the current takes when the exposed parts of
the wires touch each other.
Q23. Explain what happened to the bulb when the exposed wires momentarily
touched.
Q24. When the exposed wires were momentarily touched the path of current was
shortened (hence the term short circuit) compared to the original path which
include the bulb. What was the effect on the resistance of the circuit when the
path of current was shortened or when a short circuit occurred?
Q25. What was the effect on the current when a short circuit occurred?
Q26. Why do short circuits cause fire?
A short circuit happens when the exposed parts of the electrical wires touch
one another. When the exposed wires were made to touch, a shortened path was
provided for the current, hence the term short circuit. Since the path has been
shortened, current will no longer take the path through the bulb, thereby decreasing
the total resistance in the path of current. This will result in a large current in the
shortened circuit. Short circuits are dangerous especially with the high line voltage in
our houses (220V compare to 1.5V of dry cells) because the large current produced
can generate a lot of heat that could start a fire.
The current that a wire of given diameter can safely carry is indicated by its
current rating. When the current in the circuit exceeds the wire’s current rating, an
overload of the circuit occurs. Overloading can also generate a lot of heat in the
wire that can cause a fire outbreak.
In designing electrical installations, engineers estimate the current
requirements of appliances and electrical devices the owner intends to use and
make these as the basis for selecting the appropriate size of wire in wiring the house.
When there are too many appliances plugged into one outlet (also called
octopus wiring) the loads are effectively connected in parallel and overloading may
also occur. Figure 16 shows an example of octopus wiring.
Q27. What happens to the total resistance of the circuit when more and more
appliances are connected to one outlet?
Q28. What happens to the total current?
Q29. Overloading a circuit can start a fire. Explain.

68
Figure 16. Octopus wiring
Summary
Electric charges can only flow continuously in a complete circuit. The voltage
provides the energy that moves the charges in the circuit. The current is determined
by the voltage and the total resistance of the circuit. Current is directly proportional to
voltage but inversely proportional to resistance.
In a series circuit, the loads are connected to form a single pathway for
electric charges to pass. In a parallel circuit, the loads are connected to form
branches, each of which provides a separate path for current.
A short circuit happens when the circuit offers little or no resistance to the
flow of charges. This results in a large amount of current in the circuit. When the
current in the circuit exceeds the wire’s current rating, overload of the circuit occurs.
Link
All About Circuits. (2003-2012). Ohm’s law (again!). Retrieved from
http://www.allaboutcircuits.com/vol_1/chpt_3/4.html

69
SOUNDS
Overview
“Hey I just met you and this is crazy. So here’s my number so call me
maybe...” This is the popular song of Carly Rae Jepsen. I bet you know this song.
Can you sing the other lines? Is this the ring tone of your mobile? What about your
ring back tone? Would you want that of Maroon 5’s payphone? “Cadd9
I’m at the
payphone trying toG
call home. Em
All of my change I’ve spentDsus4
on you...” These
are cool, lovely tunes, and nice sounds.
The Science of Sound has gone all the way from a mere transfer of energy to
the creation of tunes and music for entertainment. Most of our gadgets are sound
embedded to amuse us. In the field of geology and oceanography, sound is used to
determine depths. The health sciences are also using sound for medical purposes.
Some animals are dependent on sound for movement. The newest focus of sound
science is on ecology where ecological patterns and phenomena are predicted
based on sounds released by the different components of the ecosystem. So, are
you ready to have fun with sounds?
In this module, you will learn sound propagation. While you learn about
sound, wave description and characteristics will also be introduced to you. Among
the characteristics, you will focus on the speed of sound. You will find out through
simple activities through which medium sound travels fastest. You will also find out
how the temperature of the medium affects the speed of sound. In the quest to
explore more about sound science, you will be acquainted with the properties of
waves, specifically reflection and refraction.
Through which medium does sound travel fastest- solid, liquid, or gas?
How does the temperature of the medium affect the speed of sound?
How are reflection and refraction manifested in sound?
Unit 1
MODULE
5

70
Propagation and Characteristics of Sound
Have you experienced hearing a sonic boom? Figure 1 shows a whitish cloud
at the tail end of the aircraft. This usually happens when the aircraft travels at a
speed faster than the speed of sound, i.e., the aircraft travels at supersonic speed
producing a sonic boom.
A sonic boom happens when the aircraft or any vehicle breaks the sound
barrier while it accelerates and outruns the speed of sound. A loud explosive sound
is heard on the ground and is called a sonic boom. The aircraft that does this is
usually called supersonic. There are more amazing occurrences or phenomena
related to sound. Read on and find out.
 Sound Propagation
Sound consists of waves of air particles.
Generally, sound propagates and travels through air. It
can also be propagated through other media. Since it
needs a medium to propagate, it is considered a
mechanical wave. In propagating sound, the waves
are characterized as longitudinal waves. These are
waves that travel parallel to the motion of the particles.
Do all these terms and concepts seem confusing?
Let’s try the succeeding activities to get a clearer
picture of what sound waves are.
Figure 3. Propagating Sound
Figure 2. Hearing SoundsFigure 1. Supersonic

71
Activity 1
The dancing salt and the moving beads!
Objectives:
At the end of the activity, you will be able to infer that:
1. sound consists of vibrations that travel through the air; and
2. sound is transmitted in air through vibrations of air particles
Materials:
1 rubber band
1 piece of plastic sheet
1 empty large can of powdered milk - 800 g
1 wooden ruler
1 empty small can of evaporated milk - 400 mL
rock salt
1 dowel or 1 wooden rod
1 blue bead
4 colored beads
3 inches of tape
2 large books
scissors
5 pieces of string
paper
slinky spring
transistor radio
Procedure:
Part A: Vibrations produce sound
1. Prepare all the materials needed for the activity. Make sure that you find a work
area far enough from other groups.
2. Put the plastic tightly over the open end of the large can and hold it while your
partner puts the rubber band over it.

72
3. Sprinkle some rock salt on top of the plastic.
4. Hold the small can close to the salt and tap
the side of the small can with the ruler as
shown in Figure 4.
Q1. What happens to the salt?
5. Try tapping the small can in different spots or holding it in different directions.
Find out how you should hold and tap the can to get the salt to move and
dance the most.
Q2. How were you able to make the salt move and dance the most?
Q3. What was produced when you tapped the small can? Did you observe the salt
bounce or dance on top of the plastic while you tapped the small can?
Q4. What made the salt bounce up and down?
Q5. From your observations, how would you define sound?
6. Switch on the transistor radio and position the speaker near the large can.
Observe the rock salt.
7. Increase the volume of the radio while it is still positioned near the large can.
Observe the rock salt again.
Q6. What happened to the rock salt as the loudness is increased?
Q7. Which wave characteristic is affected by the loudness or the intensity of sound?
Part B: Transmitting sound
8. Let 2 books stand up as shown in Figure 5. Place the dowel on top of the 2
books.
Figure 4

73
Figure 5. Set up for Activity 1B
9. Cut out an image of a human ear from a magazine and tape it to one of the
books.
10. Start with the blue bead. Tape the string to the mark on the dowel that is
farthest away from the ear.
11. Then tape the 4 colored beads to the other 4 marks. Make sure that all the
beads hang in a straight line.
12. The colored beads represent air particles. Create vibrations (sound) in the air
by tapping the blue bead toward the colored beads.
Q8. What happens to the other colored beads when the blue bead is tapped?
13. Create more vibrations by continuously tapping the blue bead and observe
the other beads.
Q9. Are there occasion when the beads converge then expand?
14. If the beads represent air particles, what do the converging and expanding of
the beads represent?
15. Connect one end of the slinky to a fixed point. Hold the other end then push
and pull the slinky continuously. Record your observations.
Q10. Are there converging and expanding parts of the slinky?
Q11. How then is sound classified as a wave?
16. This time shake the other end of the slinky while the other end is still
connected to the fixed point. Record your observations.
Tape ear
photo here

74
Were you able to get good sets of data from the activity? Did you enjoy
watching the salt dance and the beads move? The salt and the beads represent
particles of air when disturbed. The disturbance encountered by the salt and the
beads causes the salt to bounce up and down and the beads to move together and
spread alternately. In grade 7, you discussed that energy is transferred or
transmitted from one object to another. Bouncing salt is also a manifestation of
energy transmission. When sound is created by tapping the small can, the wave
(sound) is transmitted by air to the larger can causing the plastic cover of the larger
can to vibrate transferring energy to the rock salt. And voila!—dancing rock salt!
What about the beads? Did you observe the alternating converging and
spreading of the beads? Compare this to your observations in the slinky spring. The
converging portions of the beads match the compressions in the slinky while the
spreading portions are the rarefactions of the slinky. With the compressions and
rarefactions, what you were able to produce is called a longitudinal wave.
Longitudinal waves are waves that are usually created by pulling and pushing the
material or medium just like in the slinky (Figure 6). Alternating compressions and
rarefactions are observed. These compressions and rarefactions move along with
the direction of the pushing and pulling activity of the material or medium. Thus, the
wave moves parallel to the motion of material or the particles of the medium. This is
known as a longitudinal wave.
Figure 6. Longitudinal wave
Figure 7. Transverse wave

75
Let us compare the longitudinal wave with the other kind of wave known as a
transverse wave in Figure 7. The compressions resemble the trough while the
rarefactions are the crests. Do you still remember these characteristics of waves?
The trough is the lowest part of a transverse wave while the crest is the highest
portion. The distance from one compression to the next or between two successive
compressions in a longitudinal wave equals the wavelength. If you count the
number of compressions passing by a certain point in 1 second, you are able to
determine the frequency of the longitudinal wave. If you multiply the measured
wavelength and the computed frequency you will be able to determine the speed of
the wave. In equation,
There are other variations in the equation for the speed of the wave. The
period of the longitudinal wave is the reciprocal of its frequency . This means
that the speed of the wave can be expressed as the ratio of the wavelength and the
period,
Let us try to compare the characteristics of longitudinal wave with that of the
transverse wave in Activity 2.
Activity 2
Characteristics of waves: Comparing longitudinal
and transverse waves
Objectives:
At the end of the activity, you will be able to:
1. distinguish the different characteristics of waves;
2. determine their frequency and wavelength; and
3. compute the wave speed based on the frequency and wavelength
Materials:
Pentel pen or permanent marker
stopwatch or mobile phone
meterstick
old calendar (big poster calendar) or old newspaper
metal slinky

76
Procedure:
1. Place the old calendar or old newspaper on the floor. Make sure that the
newspaper or old calendar is long enough to accommodate the full length of
the slinky spring.
2. Put the slinky on top of the old newspaper or old calendar. Ask one of your
groupmates to hold one end of the slinky at the one end of the newspaper. This
will serve as the fixed end.
3. Another groupmate will hold the other end of the slinky. This is the movable
end.
4. The other members of the group should be along the sides so they can mark
the corresponding crests. Identify a reference point (point A) along the slinky
from which you are going to base your frequency count.
5. Shake the movable end. Apply just enough force to create large wave pulses.
Make sure, however, that the crest and trough parts will still be formed within
the newspaper area.
6. Another groupmate should count the number of pulses passing through point A
in a minute. This is the frequency in waves per minute. You can convert this
later to waves per second.
7. While your classmate is creating transverse waves by shaking the slinky, note
by marking on the newspaper the crest and the trough of the created wave
pulses.
8. Trace the wave form then measure the wavelength of the wave pulses. Record
all your data on the answer sheet provided.
9. Repeat steps 5 to 8 for two more trials. Compute for the wave speed in each of
the 3 trials. Determine also the average speed of the wave in the slinky.
10. For the second set up, repeat the whole procedure (steps 1 to 9) but this time
instead of shaking the slinky, pull and push the slinky to create a longitudinal
wave.
11. Note and mark the areas/regions in the newspaper where the slinky forms
compressions and rarefactions.
12. Count the number of compressions passing through point A in a minute. This is
the frequency of the longitudinal wave in waves per minute.
13. Measure the length between 2 compressions. This is the wavelength of the
longitudinal wave.

77
14. Do this for three more trials, and then compute for the wave speed and the
average speed of the wave in the slinky.
Q12. When there are more waves passing through the reference point in a period
of time, which wave characteristic also increases?
Q13. When there are more waves passing through the reference point in a period
of time, what happens to the wavelength of the waves?
As you have observed in Activity 2, there are many characteristics common
to both transverse wave and longitudinal wave. The difference is in the motion of
particles with respect to the direction of travel of the wave. Again, in a transverse
wave, the movement of particles is perpendicular to the direction of wave travel. In a
longitudinal wave, on the other hand, travel is parallel to the movement of the
particles (Figure 8). In longitudinal waves, compressions are created when a push is
applied on air. When air is pushed, there is a force applied on a unit area of air. From
your science in the lower grades, the force applied per unit area is called pressure.
This means that longitudinal waves are created by pressure and are also called
pressure waves. Basically, sound as you have observed it is a longitudinal wave and
a pressure wave. Just like the transverse waves, it has wave characteristics. Its
movement is parallel to the particle motion. But do the particles in a way affect the
movement of sound? What factors affect sound speed? Let us try finding this out in
the next activities.
Figure 8. Transverse and longitudinal waves

78
Activity 3
Sound race...Where does sound travel fastest?
Objective:
At the end of the activity, you will be able to distinguish which material
transmits sound the best.
Materials:
watch/clock that ticks
mobile phone
wooden dowel 80-100 cm long
metal rod 80-100 cm long
string (1 meter)
metal spoon
3 pieces zip lock bag (3x3) or waterproof mobile phone
carrying case
Procedure:
1. Hold a ticking watch/clock as far away from your body as you can. Observe
whether or not you can hear the ticking.
2. Press one end of the wooden dowel against the back part of the watch and the
other end beside your ear. Listen very well to the ticking sound. Record your
observations.
3. Repeat step #2 using a metal rod instead of the wooden dowel. Record your
observations.
Q14. Did you hear the watch tick when you held it at arm's length? When you held
it against the wooden dowel? When you held it against the metal rod?
4. Repeat steps #1 to #3 using a vibrating mobile phone instead. Record your
observations.
Q15. Did you hear the mobile phone vibrate when you held it at arm's length?
When you held it against the wooden dowel? When you held it against the
metal rod?
5. Place the mobile phone in the waterproof carrying case and dip it in a basin of
water while it vibrates.

79
Q16. Based on your observations, which is a better carrier of sound? Air or wood?
Air or water? Air or metal? Water or metal?
6. At the center of the meter long string, tie the handle of the metal spoon. Hold
the string at each end and knock the spoon against the table to make it ring or
to create a sound. Listen to the ringing sound for a few seconds then press the
ends of the strings against your ears. Observe and record the difference in
sound with and without the string pressed against your ear.
7. Knock the spoon against the table. When you can no longer hear the sound of
the ringing spoon, press the ends of the string against your ears. Record
whether or not you could hear the ringing of the spoon again.
Q17. How did the sound of the spoon change when the string was held against
your ears?
Q18. When the ringing of the spoon was too quiet to be heard through the air,
could it be heard through the string?
Q19. Is the string a better carrier of sound than air?
So, through which material does sound travel fastest? Through which
material did sound travel the slowest? Why does sound travel fastest in solids and
slowest in air? Do you have any idea what makes sound move fast in solids?
Figure 9 shows a model for the three states of matter. Identify which is solid,
liquid or gas. Now, do you have any hint why sound moves fastest in a solid
medium? To give us a better picture of the differences of the three states of matter,
consider worksheet 1. Then with the aid of Activity No.4 entitled Chimes... Chimes...
Chimes... you will be able to determine what makes solid the best transmitter of
sound.
Figure 9. A model for the three states of matter

80
Worksheet 1: Solids, Liquids, & Gases
Direction: Using several resources and references, compare the different
characteristics of solids, liquids, and gases by completing the table below.
Comparing Solids, Liquids, and Gases
Characteristics Solid Liquid Gas
Intermolecular spacing
Volume
Ability to flow
Compressibility
Density
Activity 4
Chimes… Chimes… Chimes…
Objective:
At the end of the activity, you will be able to infer using improvised chimes
that closely spaced materials are the best transmitters of sound.
Materials:
materials for chime
nylon string or thread
plastic lid or wood about 1 1⁄2 foot long
small electric fan
scissors
nail and hammer
beads
paint
iron stand

81
Procedure:
Improvised Chime
1. Go on a treasure hunt and look for items that will create a lovely sound when
they collide, such as seashells, bells, beads, spoons, forks, and stones.
2. If the items are thin enough, poke a hole through them with a nail. Then pull a
piece of string or nylon thread through each hole, and tie a knot.
3. For heavier objects, such as stones, spoons, or forks; wrap the string around
the object a few times, and rub non-toxic liquid glue over the string to hold it
in place.
4. Next, find a colorful plastic lid or a nice looking pieces of wood to serve as the
top of the wind chime.
5. Tie at least 6 of these stringed objects on the plastic lid or on the wood. Make
sure that the strands are evenly spaced and are not too far apart from each
other.
6. Finally, tie another string at the two ends of the plastic lid or on the wood for
hanging the chime.
Sounding the Chimes
1. Hang your chime in an iron stand where there is no wind source except your
handy fan.
2. With the 6 stringed objects hanging on the wooden or plastic lid, switch on
the fan and observe. This is your CHIME 1. Listen to the sound created by
your chime. Ask one of your groupmates to move away from the chime until
the sound is not heard anymore. Measure this distance from the chime to
your groupmate and record your results.
3. Repeat step #2 but add 4 more stringed objects on the chimes creating
chime with 10 stringed objects. Make sure that you tie the additional stringed
objects in between the original ones. This is your CHIME 2.
Q20. With which chime did you record a longer distance?
Q21. Which chime had more stringed objects? Which chime had more closely
spaced stringed objects given the same wooden lid?
4. Repeat step #2 but add 4 more stringed objects on the chime creating a
chime with 14 stringed objects. This is your CHIME 3.
Q22. With which chime did you record the longest distance?

82
Q23. Which chime has the most stringed objects? Which chime has the most
closely spaced stringed objects given the same wooden lid?
Q24. How would you relate the measured distance reached by the sound created
by the chime and the spacing of the stringed objects in each of the 3 chimes?
Q25. Which chime is capable of transmitting sound the best?
Q26. How would you relate the distance of the stringed objects in the chime and
the capability of the chime to transmit sound?
The speed of sound may differ for different types of solids, liquids, and gases.
For one, the elastic properties are different for different materials. This property
(elastic property) is the tendency of a material to maintain its shape and not deform
when a force is applied to the object or medium. Steel for example will experience a
smaller deformation than rubber when a force is applied to the materials. Steel is a
rigid material while rubber can easily deform and is known as a flexible material.
At the molecular level, a rigid material is distinguished by atoms and/or
particles with strong forces of attraction for each other. Particles that quickly return to
their rest position can vibrate at higher speeds. Thus, sound can travel faster in
mediums with higher elastic properties (like steel) than it can through solids like
rubber, which have lower elastic properties.
Does the phase of matter affect the speed of sound? It actually has a large
impact upon the elastic properties of a medium. Generally, the bond strength
between particles is strongest in solid materials and is weakest in gases. Thus,
sound waves travel faster in solids than in liquids, and faster in liquids than in gases.
While the density of a medium also affects the speed of sound, the elastic properties
have a greater influence on wave speed. Among solids, the most rigid would transmit
sound faster. Just like the case of wood and metal in Activity 3.
What other factors may affect the speed of sound in a medium? What about
temperature? Can the temperature of the medium affect how sound moves? Find out
in the next activity.

83
Activity 5
Faster sound… In hotter or cooler?
Objective:
At the end of the activity, you will be able to determine how temperature
affects the speed of sound.
Materials:
3 pieces 1000 mL graduated cylinders or tall containers
thermometer
bucket of ice
electric heater or alcohol lamp
tuning fork
Procedure:
1. Label the 3 graduated cylinders with HOT, ROOM TEMP, COLD respectively.
2. Half-fill the ROOM TEMP graduated cylinder with tap water.
3. Sound the tuning fork by striking it on the sole of your rubber shoes and hold it
on top of the graduated cylinder.
4. When no loud sound is produced increase the amount of water up to a level
where loud sound is produced when the vibrating tuning fork is placed on top.
Note this level of water.
5. Fill the HOT graduated cylinder with hot water (about 70o
C) to the same level
as that of the ROOM TEMP cylinder.
6. Fill the COLD graduated cylinder with COLD water (about 5O
C) at the same
level as that of the ROOM TEMP cylinder.
7. Determine the temperature of the water in each of the cylinders just before
sounding the tuning fork.
8. Sound the tuning fork in each of the cylinders and note the sound produced by
each cylinder. Record all your observations.
9. Do this for three trials focusing on the differences in the pitch of the sound each
cylinder creates. Record all your observations.

84
Q27. Which cylinder gave the loudest sound?
Q28. Which cylinder gave the highest pitched sound?
Q29. If pitch is directly dependent on frequency, then, which cylinder gives the
highest frequency sound?
Q30. Since wave speed is directly dependent on frequency, then, which cylinder
gives the fastest sound?
Q31. How would you relate the temperature of the medium with the speed of
sound?
Now you know that the speed of sound is directly affected by the temperature
of the medium. The hotter the medium the faster the sound travels. Heat, just like
sound, is a form of kinetic energy. At higher temperatures, particles have more
energy (kinetic) and thus, vibrate faster. And when particles vibrate faster, there will
be more collisions per unit time. With more collisions per unit time, energy is
transferred more efficiently resulting in sound traveling quickly. Sound travels at
about 331 in dry air at 0o
C. The speed of sound is dependent on temperature of
the medium where an increase is observed with an increase in temperature. This
means that at temperatures greater than 0o
C speed of sound is greater than 331
by an amount 0.6 of the temperature of the medium. In equation,
where T is the temperature of air in Celsius degree and 0.6 is a constant factor of
temperature. Let’s try it out at a room temperature of 25o
Celsius.

85
Properties of Sound
Figures 10 and 11 are the amazing contribution of sound to other fields such
as health, wellness and the arts particularly the music industry. We can experience
or observe these as consequences of what are commonly called properties of sound
waves. Ultrasound works on the principle of reflection of sound waves while concerts
in open field benefit from refraction of sound. Want to know more about these
amazing sound treats?
Problem: What is the speed of sound in air of temperature 25oCelsius?
Solution:
Given: T = 25oCelsius
Equation:
Solution:
Sample Problem
Figure 11. Live concertFigure 10. Ultrasound image

86
 Reflection of Sound
A lot of people love to sing inside the
bathroom because of privacy. A study
conducted noted that people would open their
mouths wide when they sing in private places
like the baths. Another reason is the hard wall
surfaces of the bathroom usually made of wood
or tiles brings about multiple reflection of sound.
These hard walls or surfaces and the small
dimension of the bathroom typically create an
aurally pleasing acoustic environment with
many echoes and reverberations contributing to
the fullness and depth of voice. Well, this may
not be the effect in the outside world though.
Look at Figure 12 and try it yourself.
Just like any other wave, sound also exhibits reflection. Reflection is
usually described as the turning back of a wave as it hits a barrier. Echo is an
example of a reflected sound. Reverberation on the other hand refers to the multiple
reflections or echoes in a certain place. A reverberation often occurs in a small room
with height, width, and length dimensions of approximately 17 meters or less. This
best fits the bathroom which enhances the voice.
In theaters and movie houses, there are also reverberations and echoes. But
these are not pleasing to the ears during a play or a movie. To lessen these,
designers use curtains and cloth cover for the chairs and carpets. Check out the
different movie houses and look for features inside that decreases reverberations
and echoes.
Echo sounding is another application of
sound reflection. This is used by scientists to
map the sea floor and to determine the depth of
the ocean or sea. This is just the same as how
bats use sound to detect distances. What about
you, can you identify other applications of sound
reflection?
Figure 12. Bathroom singing
Figure 13. SONAR

87
 Refraction of Sound
Have you ever wondered why open field concerts are usually held during
nighttime? Having concert at night gives a chance for everyone to see and enjoy the
live show because there is no work and no school. Sound also contributes to this
scheduling of concerts. Usually, sound is heard better in far areas during nighttime
than during daytime. This happens due to what is known as refraction. Refraction is
described as the change in speed of sound when it encounters a medium of different
density. As what you had earlier in this module, sound travels faster in hotter media.
This change in speed of sound during refraction is also manifested as sort of
“bending” of sound waves.
When sound propagates in air, where the temperature changes with altitude,
sound bends towards the hotter region. In this case, refraction happens. The
refraction is due to the different refractive indices of air because of the difference in
temperature. At daytime, when the sun is shining, the air near Earth’s surface is
cooler than the air above. From what you encountered in Activity 5, you learned that
sound travels faster in hotter medium. Since Earth’s surface is cooler than air above
during daytime, then sound would move from the cooler region (Earth surface)
towards the hotter air above. Thus, sound waves will be refracted to the sky (Figure
14). At night time, the air near the Earth’s surface is heated by the heat emitted by
the ground, making it hotter than the air above which is cooler due to the absence of
the sun during nighttime. This makes sound move from the cooler air above towards
the hotter air near the earth’s surface. Thus, sound waves are refracted to the
Earth’s surface (Figure15). This makes open field concerts better done during
nighttime as sound waves are refracted from the stage towards the audience. This
gives a clearer and more audible music to enjoy.
Figure15. Sound refraction at night timeFigure14. Sound refraction at day time

88
Now on a more concrete sense let us try to observe how longitudinal waves
reflect and refract. In Activity No. 6, you will be able to observe how reflection and
refraction are exhibited by longitudinal waves using our metal slinky.
Activity 6
Reflecting and refracting sound
Objective:
At the end of the activity, you will be able to observe how longitudinal waves
reflect and refract.
Materials:
metal slinky (large coil)
metal slinky (small coil)
Procedure:
Sound Reflection
1. Connect the fixed end to a wall or post. Make or create longitudinal waves by
pushing and pulling the movable end part.
2. Observe the longitudinal waves as the waves hit the wall or post. Record your
observations.
3. Note the positions of the compressions before they reach the post. Note also
the locations or positions of the compressions after hitting the wall of the post.
4. Do this for 3 trials.
Q32. What happens to the compressions or rarefactions when they hit the wall or a
fixed end?
Q33. Are the compressions found on the same location in the slinky before and
after hitting the wall?
Q34. What happens to sound waves when they hit a fixed end or the wall?

89
Sound Refraction
1. Connect the fixed end of the metal slinky (small coil) to a wall or post. Then
connect another slinky (large coil) to the other end of the small coil. Make or
create longitudinal waves by pushing and pulling the movable end of the metal
slinky (large coil).
2. Observe the longitudinal waves as the waves move from the large coil-metal
slinky to the small coil metal slinky. Record your observations.
3. Observe the frequency, amplitude, and speed of the longitudinal waves as the
waves move from the large coil metal slinky to the small coil metal slinky.
4. Do this for 3 trials.
Q35. What happens to the frequency of the longitudinal waves as the waves move
from the large coil slinky to the small coil slinky?
Q36. What would be an observable change in sound when the frequency
changes?
Q37. What happens to the amplitude of the longitudinal waves as the waves move
Q38. What happens to sound when the amplitude of the sound changes?
Q39. What happens to the speed of the longitudinal waves as the waves move
Summary
Sound waves are examples of longitudinal waves. They also exhibit
characteristic features such as frequency, amplitude, wavelength, period and wave
speed. The crest and the trough, however, are synonymous to compressions and
rarefactions. These compressions and rarefactions are created when the particles of
the medium are alternately pushed and pulled. The alternate pushing and pulling
mechanically exerts force on unit areas of air particles and thus creating pressure
waves. Compressions form when air particles or molecules of the medium are
pushed creating lesser distance between particles, while rarefactions occur when the
particles are somewhat pulled away from other particles creating a wider distance
between particles. This alternating compressions and rarefaction make up the
longitudinal waves like sound waves.

90
Just like other waves, the speed of a sound wave is determined by taking the
product of the frequency and the wavelength. Speed of sound however is dependent
on factors such as density and elasticity of the medium and temperature. The more
elastic the medium is the faster the sound travels. Likewise, a direct relation is
observed between temperature and sound speed.
Properties of waves such as reflection and refraction are also evident in
sound waves. Reflected sound is known as an echo while repeated echo in a small
dimension space or room is called reverberation. Change in speed resulting to
bending of sound or refraction are usually observed with changes in temperature at
certain altitude. What about transverse waves like light? Can we also observe these
properties? Let’s find out in the next module!
Links
Cheung Kai-chung (Translation by Yip Ying-kin). (n.d.). Why do sound waves
transmit farther at night? Is it because it is quieter at night? Retrieved from
http://www.hk-phy.org/iq/sound_night/sound_night_e.html
Gibbs, K. (2013). The refraction of sound in hot and cold air. Retrieved from
http://www.schoolphysics.co.uk/age11-
14/Sound/text/Refraction_of_sound/index.html

91
COLORS OF LIGHT
Overview
The Science of Light has gone all the way from a mere transfer of energy to
the creation of colors for entertainment and other purposes. Most of our gadgets are
light emitting for efficiency when used at night. In the field of medicine light is used to
cut through the skin for surgery as in laparoscopy. The health sciences are also
using light for other medical purposes. But the most important purpose is for humans
and other animals to see the beautiful world through light. So, are you ready to
explore the characteristics and properties of light?
In this module, you will learn some properties and characteristics of light.
Among the characteristics and properties of light, we will focus on refraction and
specifically, dispersion of light. We will try to find through simple activities how light
disperse to form the colors of light. We will also try to find the hierarchy of colors of
light in terms of frequency, wavelength, and energy. The different activities provided
in this module will make us realize the beauty of everything with light.
How are refraction and dispersion demonstrated in light?
Among the different colors of light, which is bent the most and the
least?
Why do we see spectacular events in the sky like rainbows, red
sunset and blue sky?
Unit 1
MODULE
6

92
Refraction of Light
Did you know that the boy made the stunt in a 6-ft deep swimming pool? But
as it appears in Figure 1 the water is just shallow and the stunt would not be
dangerous at all. This optical illusion is known as apparent depth. Apparent depth is
the illusion that objects under the water appear to be nearer the surface than they
really are. This is visible when an observer is standing beside the swimming pool
looking at an object under water. This phenomenon is a consequence of the bending
of light when light traverses the air-water boundary.
Figure 1. Apparent depth … Refracted light

93
Refracting Light
Light exhibits the characteristics and properties of a wave. It is classified as
an electromagnetic wave located between the spectrum of infrared and ultraviolet.
As an electromagnetic wave it does not need a medium in order to propagate. It
moves in its maximum speed in vacuum. But this speed decreases as it moves along
different media. This characteristic of light consequently shows bending when it
crosses the boundary between two media. Apparent distortion of an object seen at
the boundary between media is observed.
Figure 2. The Electromagnetic Spectrum
103
1 kilometer
100
1 meter
10-3
1 millimeter
10-6
1000 nanometer
10-9
1 nanometer
10-12 meters
700 nanometers 600 nanometers 500 nanometers 400 nanometers
Long Wavelengths Short Wavelengths

94
Figures 3 and 4 are the basic examples of refraction of light. Refraction is
the bending of light when it travels from one medium to another of different optical
densities. The pencil as shown in Figure 4 is not really broken. If we remove the
water from the glass and look at the pencil, the pencil would look normally straight.
Now try pouring water onto the glass and, voila - a broken pencil. This happens
because of the change in speed and orientation of the light with respect to the
normal as it traverses a new medium of a different density.
Figure 3. Show me the coin…
Figure 4. Broken pencil

95
Light travels so fast. From your lesson last year, it is approximated to travel at
a speed of 3 x 108
m/s in a vacuum. This speed decreases when light travels in a
dense medium. This means that the speed of light is dependent on the properties of
the medium. In the case of light, it is dependent on the optical density of the medium.
The optical density of the medium is different from its physical density. Physical
density is described as the mass per unit volume of the medium. On the other hand,
the sluggishness of the atoms of a medium to maintain the absorbed energy before
reemitting it is called optical density. When light crosses the boundary of two media
of different optical density, a change in speed takes place. This change in speed is
manifested as bending of the light ray.
Figure 5. Refraction of light

96
In Figure 6, light travels from air to water. We observe that the incident
angle (<i) is greater than the angle of refraction (<r). We can see that the light ray
refracts or bends towards the normal. Thus, light bends towards the normal when
traveling from a less dense medium to a higher density medium.
A known indicator of the optical density of a material is the index of
refraction of the material. Index of refraction represented by the symbol n is the ratio
of the speed of light in vacuum and its speed in another medium. In symbols;
𝑛 =
𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑙𝑖𝑔ℎ𝑡 𝑖𝑛 𝑣𝑎𝑐𝑢𝑢𝑚
𝑠𝑝𝑒𝑒𝑑 𝑜𝑓 𝑙𝑖𝑔ℎ𝑡 𝑖𝑛 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙
=
𝐶
𝑣
Figure 6. Refraction of Light in Water

97
The index of refraction of a material is a quantity that compares the speed of
light in that material to its speed in a vacuum. Since the speed of light in vacuum is
the highest attainable speed in the universe, the index of refraction is always greater
than 1. The n values of other media are shown in Table 1.
Table 1. Index of refraction of other materials
Materials Index of Refraction
Diamond 2.147
Zircon 1.923
Light flint glass 1.580
Crown glass 1.520
Ethyl alcohol 1.510
Water 1.360
Ice air 1.310
Vacuum 1.000

98
Activity 1
The colors of the rainbow...The colors of light
Objectives:
1. white light is made up of many different colors of light; and
2. each of these colors of light bends differently when it strikes objects like a
prism.
Materials:
a sunny window
plastic container filled with water
2 sheets of white paper
a small mirror
penlight
prism
stack of books
Procedure:
Part A: ROY G. BIV on paper using a bowl of water
1. Place the bowl near the window. Make sure
that there is plenty of sunlight in that part of the
window.
2. Set the mirror partway into the water facing the
light as shown in the figure on the right.
3. Hold the piece of paper up to intercept the
reflected beam.
4. Adjust the position of the mirror until you see color bands on the piece of paper.
Q1. List and arrange the observed colors according to how they appear on the
paper.

99
Part B: ROY G. BIV using a prism
1. Position a stack of books near the window where there is plenty of sunlight.
2. Place a white sheet of paper on top of the stack of books.
3. On top of this sheet place the prism. Make sure that sunlight from the window
reaches the prism.
4. Position the prism until a rainbow or the colors of light appear on the white
sheet of paper.
5. Use the table below to note the refractive indices of the colors of light in acrylic
or crown glass
Material/Color of light (nm) n
Acrylic
 Red
 Orange
 Yellow
 Green
 Blue
 Violet
650
600
550
500
450
400
1.488
1.490
1.497
1.495
1.502
1.508
Crown Glass
 Red
 Orange
 Yellow
 Green
 Blue Violet
650
600
550
500
440
400
1.512
1.515
1.518
1.520
1.525
1.530
6. Record all your observations in the worksheet provided.

100
Q2. Describe the position of the different colors after passing through the prism
Q3. Explain the dispersion of white light. Why is the prism or water able to separate
the colors of white light?
Q4. Compare your results in the first part with your results in the second part. Are
there any differences? What might account for the differences?
Q5. What did you observe with the indices of refraction of the colors of light in the
acrylic prism?
Q6. How would this indices of refraction account for the arrangement of colors of
light?
Were you able to get good sets of data from the activity? Did you enjoy
watching how the rainbow colors appear when white light strikes the prism or the
mirror in the bowl of water? We highlight here the arrangement of colors of light as
ROYGBIV when dispersion happens. Again, dispersion is a special kind of refraction
which provided us colors of light. This phenomenon is observed when white light
passes through a triangular prism. When white light enters a prism, separation into
different colors is observed. Remember the concept of refractive indices in the
previous module and in the first part of the lesson? The refractive indices of the
different colors of light indicate that light of different colors travels at different speeds
in the prism which accounts for the different degrees of bending. Thus, blue light with
greater refractive index refracts more and appears at the bottom of the red light.
Activity 3, however, will give you a better idea why this is so.

101
Activity 2
Red versus violet...
Objectives:
At the end of the activity, you will be able to observe that bending depends on
the refractive index of the color of light.
Materials:
2 sheets of white paper
a small mirror
flashlight
prism
Procedure:
1. Place or position two glass prisms on top of a white sheet of paper and near a
white screen. It would be better if the white screen is positioned vertically.
2. Position a flashlight on the other side of the prism. Switch on the flashlight and
let the light strike the mirror.
3. Make the necessary adjustment in the position of the prism or in the position of
the flashlight until you observe a clear view of the different colors of light on the
screen.
4. Mark the position of the colors of light on the white screen. Mark also the
positions of the flashlight and the prism on the white sheet of paper.
5. Trace the light beam from the flashlight to the prism. Then trace the light ray
from the prism to each of the colors of light on the white screen.
6. Draw line AO that bisects the prism located near the white screen vertically.

102
Q7. Did you observe the colors of light just as they appeared in the first activity?
Q8. How were these colors of light arranged on the white screen?
Q9. With respect to line AO, which among the colors of light on the white screen is
most bent, red light or blue light?
Below is a table of wavelength and refractive indices of the color of light in a
crown glass prism.
Acrylic
 Red
 Orange
 Yellow
 Green
 Blue
 Violet
650
600
550
500
450
400
1.488
1.490
1.497
1.495
1.502
1.508
Crown Glass
 Red
 Orange
 Yellow
 Green
 Blue
 Violet
650
600
550
500
440
400
1.512
1.515
1.518
1.520
1.525
1.530

103
Q10. How would you relate the refractive index with the bending of the color of
light?
But what does the hierarchy of colors of light exhibit in terms of energy?
Which color of light has the greatest energy? The next activity (Activity No. 4) will
provide you with answers to this question. In this activity, you will be able to relate
the hierarchy of colors and the hierarchy of the corresponding energy.
Activity 3
Which color has the MOST energy?
Objectives:
1. energy of the colors of light increases as one goes towards the right side
of the color spectrum; and
2. red light has the least energy and blue light has the most energy.
Materials:
six (6) thermometers (special thermometers which are sensitive to small
changes in temperature)
colored plastic (half sheets of Red, orange, yellow, green, blue and violet)
stapler
scissors
Scotch tape
string (nylon)
intense light source (if it is not sunny)
Procedure:
1. First, hang these thermometers in a shaded area. Wait for 10 minutes, then
quickly observe and record the temperature shown by each thermometer. This
will serve as the initial temperature of the thermometers. Wrap each
thermometer with a different colored plastic. You may use Scotch tape to
secure the thermometer.

104
2. Connect strings at the end part of the thermometer.
3. Then hang the thermometers with their respective wraps directly under the sun
or an intense light source.
4. Record the temperature readings in each thermometer every five minutes.
Time
Interval
Temperature Readings (o
C)
Red Orange Yellow Green Blue Violet
Initial T
Ist 5 min
10 min
15 min
20 min
25 min
30 min
Average
Q11. Which thermometer registered the lowest temperature?
Q12. Which thermometer registered the highest temperature?
Q13. Which colored plastic allowed more energy to pass through it?
Q14. Which colored plastic allowed the least energy to pass through it?
Q15. From your answers in Q13 and Q14, which color of light has the least
energy? The most energy?

105
Did you have a good set of results? Were you able to enjoy the activity on the
energy of colors of light? Temperature as we have defined it in the previous module
is the average kinetic energy of the molecules of an object. The higher the registered
temperature, the greater is the average kinetic energy. When the violet colored
wrapper is hit by sunlight or a light source, only the violet component of white light
passes through the plastic. Since the thermometer wrapped in violet plastic
registered the highest temperature, violet light then greatly increases the average
kinetic energy of the air surrounding the thermometer. On the other hand, the
thermometer with the red plastic cover only allows red light to pass through it. This
means that since the thermometer covered with the red plastic sheet registered the
lowest temperature, red light only brings about a minimal increase in the average
kinetic energy of the air surrounding the thermometer. Basically, from Activity 3, we
have identified that blue has the highest energy and red light has the least. On which
other characteristics of color of light does the energy of the colors of light depend
on?
Activity 4 revisits the activity you have already done in Grade 7. The focus of
the activity in Grade 7 however, was to identify the corresponding frequency and
wavelength of each color of light and the computation of the speed of each. We
noted last time that the speed of the wave is the product of the frequency of the wave
and the corresponding wavelength. This time we will focus on how energy relates to
the frequency of the colors of light.
Activity 4
The color spectrum wheel revisited
Objectives:
1. light is composed of colors of different frequencies and wavelength;
2. the frequencies of the colors of light are inversely proportional to the
wavelength;
3. the product of the frequency and the wavelength of the colors of light is a
constant; and
4. the arrangement of colors of light shows the hierarchy of the color’s
corresponding energy.

106
Materials:
Color Spectrum Wheel Pattern Cardboard or illustration board
white screen
button fastener
glue or paste
Procedure
Part 1: Color Wheel
1. Cut the two art files that make up the wheel on the next pages.
2. Cut along the lines drawn on the top wheel. Cut the 2 sides as shown. The
small window near the center of the wheel should be completely cut out and
removed.
3. Punch a hole at the center of the two wheels. You may use a button fastener to
secure the two wheels together one on top of the other, but they should be free
to rotate relative to each other.
4. When you see a region of the color spectrum show up in the open window and
the "W,F, E" that correspond to that region showing up under the flaps, then
you know that you have done it right.

109
Part 2: Characteristics of Light
1. Try out your Color Spectrum Wheel by positioning the innermost of the flaps on
COLOR SPECTRUM. This will simultaneously position the other flaps to
WAVELENGTH, FREQUENCY, and ENERGY.
2. Turn the upper wheel and observe the combinations.
3. Fill in the table below with the corresponding combinations you have observed
using your Spectrum Color Wheel.
Frequency
(Hz)
Wavelength
(m)
Frequency x
wavelength
Energy
(eV)
Red
Orange
Yellow
Green
Blue
Violet
4. You will need to convert the equivalents of frequencies to Hz, the equivalent
wavelengths to meters, and Joule to eV.
Note the following equivalents:
 Terra (T) is a prefix for 1012
(1 THz = 1 x 1012
Hz)
 nano (n) is a prefix equivalent to 10-9
(1 nm = 1 x 10-9
m)
 1 eV = 1.6 x 10-19
Joule
Q16. Which color registered the highest frequency? shortest wavelength?
Q17. Which color registered the lowest frequency? longest wavelength?
Q18. What did you observe about the wavelengths and frequencies of the different
colors of light?
Q19. What did you observe about the products of frequencies and wavelengths?
Q20. Does the frequencies of the colors of light increase from Red to Violet?
Q21. What did you observe about the corresponding energies from Red to Violet?
Q22. How is frequency relate to energy of colors of light?

110
Now you have an idea why rainbows appear the way they do. Rainbows are
created just like the colors of light appeared in Activity 1. A prism is needed to break
the white light into the different colors of light. With the different refractive indices of
the colors of light, bending is also different for each of the colors of light. From
Activity 2 you have just found that Blue light is bent most. Thus, a rainbow starts with
the RED light being at the topmost and ends with the VIOLET light being on the
bottom of the bow? However, you saw the Blue at the bottom since Violet light is not
very visible. But which acts as a prism in the sky for real large rainbows to form? Do
you still believe that there is really a pot of gold at the end of the bow? There are
many other beliefs about what we usually observe in the sky. Are these really true?
Do they have scientific bases? Can you explain these phenomena? Let’s try Activity
5.
Activity 5
Scientific explanations behind certain beliefs
Objectives:
At the end of the activity, you will be able to come up with a presentation of
the scientific explanations of certain superstitious beliefs related to observable
phenomena in the sky.
Materials:
interview guide
pen and paper
Procedure:
1. With your groupmates, draft about 5 questions that you intend to ask people so
that you will be able to get information about your beliefs of the people in the
locality regarding the following phenomena:
a. Red sky in the afternoon (sunset)
b. Why the sky is blue
c. There’s a pot of gold at the end of the rainbow
2. After writing the draft interview questions, have the questions checked by your
teacher.
3. With the interview guide, visit old folks and conduct interviews.

111
4. Discuss with your groupmates the basic scientific explanations behind the
superstitious beliefs. Complete the table in the worksheet.
5. You need to come up with a creative way of showing scientific explanations
about the phenomena mentioned above in any form: electronic, play, or
simulations.
Rubric Scoring Guide
CATEGORY 4 3 2 1
Presentation
(50%)
Well-rehearsed with
smooth delivery that
holds audience
attention.
Explanations
presented are easy
to follow and there is
no script reading or
definition reading
during the
presentation.
Props used are very
useful during the
presentation
Rehearsed with fairly
smooth delivery that
holds audience
attention most of the
time. Explanations
presented are easy
to follow and there is
script reading or
definition reading
during the
presentation.
Delivery not smooth,
but able to maintain
interest of the
audience most of the
time. Explanations
presented not very
easily understood
and there is script
reading or definition
reading during the
presentation.
Delivery not smooth
and audience
attention often lost.
Explanations are
very vague and the
presenters settle with
reading the whole
presentation.
Interview
Guide
(15%)
Questions are very
appropriate to
determine
information about
superstitious beliefs
of folks
There are no
grammatical of
spelling errors.
Questions are
appropriate to
determine
information about
of folks
There are few
grammatical of
spelling errors.
Questions are
somewhat
appropriate to
determine
information about
of folks
There are many
grammatical of
spelling errors.
Questions NOT
appropriate to
determine
information about
of folks
There are many
grammatical of
spelling errors
Table of
Superstitious
beliefs and
Scientific
Explanation
(35%)
Superstitious beliefs
listed are empirically
based.
Scientific
explanations are
accurately stated
Most of the
based.
Scientific
explanations are
somewhat accurately
stated
Some of the
based.
Scientific
explanations are
somewhat accurately
stated
Almost all of the
based.
Scientific
explanations not
accurately stated.
There are many
misconceptions
identified in the
explanations

112
Summary
The dual nature of light brings about several observable phenomena in the
sky. Light as a wave exhibits properties just like any other waves. When light moves
from one medium to another of a different density, the speed changes, bringing
about changes in the direction of the refracted ray with respect to the normal line.
This is known as refraction. Refraction of light, however, may result in a display of
colors of light when it passes through materials that can have varied refractive
indices for every wavelength of color that passes through them. A glass prism, for
example, has varied refractive indices per wavelength of color resulting in different
bending angles of the refracted colors of light with respect to the normal line. This
phenomenon is better known as dispersion.
With the concept of dispersion, colors of light are hierarchically arranged as
ROYGBIV according to frequency and energy of the colors of light. Red happens to
have the lowest frequency and the least energy. Energy and frequency increases as
one moves from red light towards violet light. This display of colors of lights by
dispersion of white light is one of the consequences of refraction of light aside from
the apparent depth mentioned above. Other consequences are spectacular
phenomenon of blue skies and red sunsets.
What other properties of light can be observed? Excited to know? These will
be introduced to you at the next level! In the meantime, relax and enjoy the next
module.
Hewitt, Paul. (1989). Conceptual physics (6th
Ed.) London: Scoot, Foresman and
Company
Hwang, Fu-kwun. (n.d.). Colors. Retrieved from http://users.hal-
pc.org/~clement/Simulations/Mixing%20Colors/rgbColor.html
Georgia State University. Department of Physics and Astronomy. (2013). Retrieved
from http://www.phy-ast.gsu.edu.
Release the rainbow. (2013). Retrieved from
http://www.optics4kids.org/home/futurescientists/easy/release-the-rainbow/
Tracing, R. (n.d.). S369 AP physics. Retrieved from
http://www.shs.d211.org/science/faculty/MJP/s369/light/docs/RayDiagrams.htm

113
UNIT 2
Earth and Space
NNAASSAA EEaarrtthh OObbsseerrvvaattoorryy

115
EARTHQUAKES AND
FAULTS
Overview
If you recall, it was mentioned in Grade 7 that the Philippines is located along
the Ring of Fire. How does this affect us? People who live along the Ring of Fire
have to put up with earthquakes and volcanic eruptions. In this module, we will focus
on earthquakes.
An earthquake is one of the most frightening things that anyone can ever
experience. You grow up believing that the Earth is rock solid and steady. But then
the ground suddenly shakes and you do not know what to believe anymore.
Strong earthquakes have caused countless deaths all over the world, even
before people have started recording these events. No wonder scientists have been
working very hard to find a way to predict when an earthquake occurs.
No one can stop quakes from happening. But there are things that people
can do to avoid or reduce loss of life and damage to property. The first step is to
have a clear understanding of the occurrence of earthquakes.
Why do earthquakes occur?
What is the relationship between earthquakes and faults?
Unit 2
MODULE
1
Suggested time allotment: 15 hours

116
What is a Fault?
On July 16, 1990, a strong earthquake hit Luzon. Have you heard about it?
Maybe not, because it happened before you were born. But if your parents are from
Luzon, they surely know about the earthquake. It is possible that they were even
affected by it.
During that earthquake, many people lost their lives and many more were
injured. A lot of buildings and other structures were either damaged or destroyed.
The earthquake had a magnitude of 7.8 and its epicenter was located in Nueva Ecija.
According to scientists, the earthquake was caused by movement along the
Philippine Fault.
Fault, epicenter, magnitude. Do you know what these terms mean? You will
learn about them in this module. Let us start with faults.
Earthquakes are associated with faults. When a fault suddenly moves, an
earthquake occurs. Do you know what a fault is? Do the following activity to find out.
Activity 1
A fault-y setup
Objectives:
1. describe the appearance of a fault; and
2. explain how a fault forms.
Materials Needed:
two sheets of cardboard (or folder)
fine sand
ruler
newspaper (or plastic sheet ) as wide as a newspaper page

117
Procedure:
1. Spread the newspaper on a table. Do the activity on the newspaper.
2. Arrange the two sheets of cardboard edge to edge (Figure 1).
3. Pour sand along the boundary of the two sheets (Figure 2).
Figure 1. Cardboard sheets placed side by side.
Figure 2. Sand along the boundary.

118
4. With the ruler, flatten the top of the sand and make two parallel lines.
5. Now, move the sheets slowly in the direction shown in Figure 3.
Q1. As you move the sheets, what is formed in the sand?
Q2. What happens to the lines?
Now, study Figure 4. Do you see anything unusual?
Figure 3. Top of sand flattened.

119
If you look at the picture carefully, you can guess that the road was originally
in one piece. But the road is no longer continuous. There is a cut across the road
and now there are two sections. One section has moved with respect to the other.
Compare what you see in the picture and what you saw in the activity. Is
there something in the picture that looks like what was formed in the activity? Do you
see anything similar?
Based on the activity and the picture, you can probably guess what a fault is
by now. A fault is a break in the Earth’s crust, and along the break, significant
movement has taken place.
Figure 4. Can you spot the fault? (Image courtesy of the GEER Association and
National Science Foundation)

120
How do Faults Produce Quakes?
In the following activity, you will learn how earthquakes are related to faults.
Activity 2.
Stick ‘n’ slip
Objectives:
1. explain how faults generate earthquakes; and
2. explain why not all movement along faults produces earthquakes.
Materials Needed:
two small boxes (fruit juice boxes are ideal)
masking tape
rubber band
paper clip
Procedure:
1. Attach the rubber band to the paper clip. Then attach the paper clip to one
end of one box. (See Figure 5. The ruler is included for scale.)
Figure 5. Two boxes - one with a rubber band
attached to a paper clip

121
2. Place the boxes side by side. Put a toy house on the box with the rubber
band. Then tape (lightly?) the two boxes together as shown in Figure 6.
Important: Do not stick the tape on the boxes too much. The tape is meant to
come off.
Figure 6. Two boxes side by side and
lightly taped. Toy house on top of box with
rubber band)
Figure 7. Rubber band on box with toy
house pulled slowly. Observe what
happens.

122
3. With your left hand, hold the box without the rubber band in place. With your
other hand, slowly pull on the rubber band in the direction shown in Figure 7.
Q3. What happens to the rubber band?
Q4. Keep on pulling on the rubber band. What happens to the box attached to the
rubber band? Note: The tape is supposed to come off, so stick it on very
lightly.
Q5. What happens to the “house”?
Q6. Which is the “fault” in this setup?
Imagine the boxes as the ground, and the boundary between them as a fault.
Energy from inside the Earth makes the ground move. You simulate this by pulling
on the rubber band. There is no movement right away because of friction. (What
represents friction in the activity?)
Once friction is overcome, the ground suddenly moves and an earthquake
occurs. Some scientists describe this process as stick and slip. At first, the rocks are
stuck together due to friction. Later, the rocks suddenly slip, generating an
earthquake. Every time a fault slips, the Earth quakes.
In the activity, there was a sudden jerk, but no shaking. The boxes did not
shake as in a real earthquake. Let us see what the next model does (shows?).
Activity 3.
Stick ‘n’ shake
Objectives:
1. explain the effect of bending of rocks along faults, and
2. relate faults movement and earthquakes

123
Materials Needed:
two plastic rulers
a bit of clay
Procedure:
1. Using the clay, attach the rulers’ ends together (how long is the overlap
between rulers?) (Figure 8 shows closeup photos of side and top views of
the setup.)
2. Hold the rulers as shown in the picture below. Then slowly move your hands
in the direction of the arrows.
Q8. What happens when bending becomes too much? Note: If nothing
happens, separate the rulers and re-attach them only slightly.
Figure 8. Side view and top view of setup.
Figure 9. Right hand pushes
(arrow up) while left hand
pulls (arrow down)
Figure 10. What is stored in the
bent rulers?

124
The activity you just performed simulates how rocks bend along a fault. Think
of the rulers as if they were part of the ground. Figure 11 can help you visualize this.
Drawing A shows how the rocks look at first. Then energy from inside the
Earth makes the rocks bend (Drawing B). But as mentioned earlier, the rocks along
the fault do not move immediately. Friction keeps them in place. (In the activity, what
represents friction?)
When too much bending occurs and the limit is reached, the rocks suddenly
snap (Drawing C). The bent rocks straighten out and vibrate. The vibrations travel in
all directions and people in different places will feel them as a quake. An earthquake
is a vibration of the Earth due to the rapid release of energy.
Figure 11.
Drawing A shows
the ground before
bending. In
Drawing B, the
ground is bending,
storing energy. In
Drawing C, the
bending limit is
reached, and the
ground has
snapped.

125
Focus and Epicenter
Now that you know the relationship between faults and earthquakes, it is time
to get to know the meaning of terms used when earthquakes are reported in the
news.
Activity 4.
Where does an earthquake start?
Objectives:
1. differentiate between focus and epicenter; and
2. demonstrate how movement along faults affect the surroundings.
Materials Needed:
fault model
scissors
paste
Procedure:
1. Photocopy the Fault Model (Figure 12; you can also trace it on paper). Then
cut along the outlines of the two drawings.
2. Fold along the lines and paste where indicated. In the end, you should have a
model consisting of two parts that fit together (Figure 13).
3. The upper surface of the model represents the surface of the Earth. The trace
of the fault on the surface of the Earth is called the fault line. Be ready to point
out the fault line when your teacher calls on you.
4. Pull the two pieces apart (Figure 14). The flat surface between the two pieces
is called the fault plane. This is where fault slip or fault movement happens.
Point out the fault plane when your teacher asks you.
5. The place where the fault begins to slip is called the focus. It is where the first
movement occurs. Thus, the focus is the origin of the earthquake. Be ready to
explain it to your teacher.

127
6. Put the two pieces of the model together. The focus is now hidden
“underground.” Now, imagine a vertical line from the focus to the upper
surface of the model. Mark the place where you expect the line to come out.
The spot directly above the focus on the surface of the Earth is called the
epicenter. Show the “epicenter” of your model to your teacher.
Q9. Use your model to show different types of movement along a fault. How
would the surroundings be affected?
How Strong is the Earthquake?
An earthquake may be described in two ways: intensity and magnitude. The
intensity of an earthquake gives us an idea of how strong or weak the shaking is.
The Philippine Institute of Volcanology and Seismology (PHIVOLCS) uses the
following scale to describe the intensity of earthquakes in the Philippines.
Figure 13. (Left) The fault model is made of two parts that fit together.
(Right) The flat surface between the two parts represents the fault
plane.

128
Table 1. PHIVOLCS Earthquake Intensity Scale (PEIS)
Intensity
Scale Description
I
Scarcely Perceptible - Perceptible to people under favorable
circumstances. Delicately balanced objects are disturbed slightly.
Still water in containers oscillates slowly.
II
Slightly Felt - Felt by few individuals at rest indoors. Hanging
objects swing slightly. Still water in containers oscillates noticeably.
III
Weak - Felt by many people indoors especially in upper floors of
buildings. Vibration is felt like one passing of a light truck. Dizziness
and nausea are experienced by some people. Hanging objects
swing moderately. Still water in containers oscillates moderately.
IV
Moderately Strong - Felt generally by people indoors and by some
people outdoors. Light sleepers are awakened. Vibration is felt like
a passing of heavy truck. Hanging objects swing considerably.
Dinner, plates, glasses, windows, and doors rattle. Floors and walls
of wood framed buildings creak. Standing motor cars may rock
slightly. Liquids in containers are slightly disturbed. Water in
containers oscillate strongly. Rumbling sound may sometimes be
heard.
V
Strong - Generally felt by most people indoors and outdoors. Many
sleeping people are awakened. Some are frightened, some run
outdoors. Strong shaking and rocking felt throughout building.
Hanging objects swing violently. Dining utensils clatter and clink;
some are broken. Small, light and unstable objects may fall or
overturn. Liquids spill from filled open containers. Standing vehicles
rock noticeably. Shaking of leaves and twigs of trees are noticeable.
VI
Very Strong - Many people are frightened; many run outdoors.
Some people lose their balance. Motorists feel like driving in flat
tires. Heavy objects or furniture move or may be shifted. Small
church bells may ring. Wall plaster may crack. Very old or poorly
built houses and man-made structures are slightly damaged though
well-built structures are not affected. Limited rockfalls and rolling
boulders occur in hilly to mountainous areas and escarpments.
Trees are noticeably shaken.

129
VII
Destructive - Most people are frightened and run outdoors. People
find it difficult to stand in upper floors. Heavy objects and furniture
overturn or topple. Big church bells may ring. Old or poorly-built
structures suffer considerably damage. Some well-built structures
are slightly damaged. Some cracks may appear on dikes, fish
ponds, road surface, or concrete hollow block walls. Limited
liquefaction, lateral spreading and landslides are observed. Trees
are shaken strongly. (Liquefaction is a process by which loose
saturated sand lose strength during an earthquake and behave like
liquid).
VIII
Very Destructive - People are panicky. People find it difficult to
stand even outdoors. Many well-built buildings are considerably
damaged. Concrete dikes and foundation of bridges are destroyed
by ground settling or toppling. Railway tracks are bent or broken.
Tombstones may be displaced, twisted or overturned. Utility posts,
towers and monuments may tilt or topple. Water and sewer pipes
may be bent, twisted or broken. Liquefaction and lateral spreading
cause man-made structure to sink, tilt or topple. Numerous
landslides and rockfalls occur in mountainous and hilly areas.
Boulders are thrown out from their positions particularly near the
epicenter. Fissures and faults rupture may be observed. Trees are
violently shaken. Water splash or slop over dikes or banks of rivers.
IX
Devastating - People are forcibly thrown to ground. Many cry and
shake with fear. Most buildings are totally damaged. Bridges and
elevated concrete structures are toppled or destroyed. Numerous
utility posts, towers and monument are tilted, toppled or broken.
Water sewer pipes are bent, twisted or broken. Landslides and
liquefaction with lateral spreadings and sandboils are widespread.
the ground is distorted into undulations. Trees are shaken very
violently with some toppled or broken. Boulders are commonly
thrown out. River water splashes violently or slops over dikes and
banks.
X
Completely Devastating - Practically all man-made structures are
destroyed. Massive landslides and liquefaction, large scale
subsidence and uplift of land forms and many ground fissures are
observed. Changes in river courses and destructive seiches in large
lakes occur. Many trees are toppled, broken and uprooted.

130
The intensity of an earthquake is determined by observing the effects of the
earthquake in different places. Houses, buildings, and other structures are inspected.
People are interviewed about what they saw (the cabinet fell over), how they felt (I
was frightened), or what they did (I ran out of the house).
Now, do the following thought exercise. Suppose an earthquake occurred in
Luzon. Would the intensity be the same all over the Philippines? Before you tackle
this question, try answering the following first:
A) When an earthquake occurs, where would shaking be greater? Near the
epicenter or away from the epicenter?
B) Where would damage be more? Near the epicenter or away from the
epicenter?
C) Based on your answers to Questions A and B, where would the
intensity be higher? Near the epicenter or away from the epicenter?
Another way of describing the strength of an earthquake is by magnitude.
Recall that as rocks bend along a fault, energy is stored little by little. When the rocks
suddenly snap, the stored energy is released.
The released energy can be calculated by scientists and is called the
magnitude of the earthquake. Obviously, the greater the magnitude, the stronger the
earthquake. To distinguish the two, intensity is expressed using Roman numerals (I,
II, III) while magnitude uses Hindu-Arabic numerals (2, 3, 4).
Earthquakes with a magnitude of 2 may or may not be felt. Those that are felt
by most people have a magnitude of 4. Magnitude 6 quakes can lead to a lot of
damage in highly populated areas.
Earthquakes with a magnitude of 7 can cause severe damage. A magnitude
8 or 9 quake results in widespread destruction, especially near the epicenter. Luckily,
only one or two occur every year.

131
Do You Live Near an Active Fault?
An active fault is one that has moved in the past and is expected to move
again. Put in another way, an active fault has generated earthquakes before and is
capable of causing more in the future.
Scientists use different ways to find out if a fault is active. One is by checking
the country’s historical records. Historians always write about destructive events
such as earthquakes.
Another is by studying the vibrations, past and present, that come from faults.
Still another way is by observing the surroundings. For example, a fault may cross a
road and because of that, the road is displaced.
Or a fault may cut across a stream and the stream channel is then shifted. Or
a fault may slice through mountains and form cliffs. This is not to say that anyone
can spot an active fault. Scientists need a lot of training to do that.
But along some faults, the effects may be dramatic. Suppose a house was
built on a fault. As the ground shifts little by little, parts of the house will be affected.
The floor will crack, doors will not close, and the roof may start to leak.
Obviously, it is important to know the location of active faults. As far as
possible, no important structures should be built near or on them. PHIVOLCS has a
map that shows the active faults in the Philippines (Figure 14).
(In the map, the lines with triangles are trenches, another source of
earthquakes. Trenches will be discussed in Grade 10.)
Study the map and find out where you live. Is there an active fault passing by
your town, province, or region? If so, are you and your family prepared for the
occurrence of an earthquake?

132
Figure 14. Active Faults and Trenches

133
Earthquakes and Tsunamis
In March 2011, a powerful earthquake took place in the Pacific Ocean near
Japan. Afterward, a tsunami hit Japan. Tens of thousands (please check
approximate figures) Twenty thousand people were killed. More than a million
houses and buildings were damaged or destroyed.
In December 2004, a strong earthquake occurred in the Indian Ocean near
Indonesia. A tsunami soon followed. More than 200,000 people were confirmed
dead, many of them in Indonesia, Thailand, India, and Sri Lanka.
In 1976, an earthquake took place in the Moro Gulf in Mindanao. Later on, a
tsunami hit nearby coastal areas. Thousands of people were killed. Many more were
declared missing.
What is the connection between earthquakes and tsunamis?
Activity 5.
Tsunami!
Objectives:
1. explain how tsunamis are generated; and
2. infer why tsunamis do not always occur even when there is an
earthquake
Materials Needed:
flat basin or laundry tub (batya)
water
rectangular piece of plastic panel or plywood
rock

134
Procedure:
1. Put water in the container. Place the rock in the water at one end of the
container (Figure 15).
2. At the other end of the container, put the plastic panel flat at the bottom of the
container (Figure 16, left).
3. You will need some help: a person to watch the surface of the water, and
another to watch the level of water by the rock. Things will happen quickly, so
make sure your assistants are alert.
4. Hold the corners of the plastic panel with your thumbs and fingertips. Wait for
the water to stop moving. Using only your fingertips, jerk the edge of the
plastic board upward (Figure 16, right).
Q10. What was formed in the water by the sudden push of the plastic panel?
Q11. How was the water level by the rock affected by the wave?
Figure 15. Setup for the tsunami activity
Figure 16. (Left) The plastic panel placed flat at the bottom of the container.
(Right) Wait for the water to stop moving, then suddenly jerk the edge of the plastic
panel upward (see white arrow).

135
Q12. What does the water represent? How about the rock?
Q13. What does the plastic panel represent?
Faults are found not only on land but also under the sea. When a fault at the
bottom of the sea suddenly moves, the water above it can be affected. A sudden
push from an underwater fault can produce a wave called a tsunami.
Unlike a wave that is formed by the wind, a tsunami is so much more
powerful. Wind waves are just sea-surface waves. In comparison, a tsunami involves
the whole depth of the sea, from the seafloor to the surface.
Far from the shore, a tsunami is low, maybe just a meter high. But it travels at
the speed of a jet plane. When the tsunami reaches the shore, it slows down but it
grows in height.
A tsunami is very destructive because the force of the whole ocean is behind
it. This is the reason why whole towns and cities are totally devastated after a
tsunami attack.
So, how are earthquakes related to tsunamis? When a fault suddenly moves
on land, you get an earthquake. But if a fault suddenly moves in or near a body of
water, you may get a tsunami in addition to the earthquake.
Thus, when you are near the sea and you feel a strong earthquake, treat that
as a warning signal. Run to the highest place you can find, or if you have a vehicle,
evacuate inland.
Not every fault movement beneath the sea will produce a tsunami. Those
faults that move in a horizontal direction or sideways will not result in a tsunami. The
fault has to move in the vertical sense. In the activity, a sudden upward push
triggered the wave.
What’s Inside the Earth?
We often think of earthquakes as something harmful and the reason is
obvious. But earthquakes help scientists figure out what is inside the Earth. How? As
you know by now, when a fault suddenly moves, an earthquake is generated.

136
The shaking starts from the
focus and spreads out. You can get an
idea of how this happens by throwing a
pebble into a pond. See the ripples that
move out in circles? The vibrations
from the focus are something like that.
The vibrations are more
properly called seismic waves. As
seismic waves travel through the body
of the Earth, they behave in different
ways, depending on what they
encounter along way (Figure 17).
For example, as seismic waves
travel deeper into the crust, they speed
up. That means that at depth the rocks
are denser. In the upper part of the
mantle, the waves slow down. That
means the rocks there are partially molten.
As the waves reach the core, one kind of seismic wave (s-waves) disappears.
That means that the outer core is liquid. At certain depths, the waves are reflected
and refracted (bent). That means the Earth must be layered.
Thus, earthquake waves give us a picture of the Earth’s interior, the way an
“ultrasound” provides an image of a baby inside the womb. This is why scientists
know a bit about the interior of our home planet, even if no one has gone deep into
the Earth yet.
Tarbuck, E.J., & Lutgens, F.K. (1999). Earth, An Introduction to Physical Geology (6th
ed.). Upper Saddle River, NJ: Prentice Hall.
http://earthquake.usgs.gov/
http://www.phivolcs.dost.gov.ph/
http://www.geerassociation.org/GEER_Post%20EQ%20Reports/Duzce_1999/kaynas
li1.htm
Figure 17. The behavior of seismic
waves reveals what the Earth looks like
inside.

137
UNDERSTANDING
TYPHOONS
Overview
Every year the Philippines is hit by typhoons. No part of the country is spared.
All provinces have been visited by a typhoon at one time or another. In recent years,
the Philippines had been overwhelmed by powerful tropical cyclones.
Who could forget the terrible flood brought by Tropical Storm Ondoy in 2009?
Or the people swept out to sea during Tropical Storm Sendong in 2011? Or the poor
community of New Bataan buried in mud spawned by Typhoon Pablo in 2012?
According to the Philippine Atmospheric, Geophysical, and Astronomical
Services Administration (PAGASA), about 20 tropical cyclones enter the Philippine
Area of Responsibility each year. We have to be knowledgeable about tropical
cyclones if we want to prevent the loss of more lives.
Why is the Philippines prone to typhoons?
What conditions favor the formation of typhoons?
Unit 2
MODULE
2

138
What is a Typhoon?
We all know what a typhoon is. Or more accurately, we know what to expect
when a typhoon comes. We get a lot of rain and strong winds. Now, you may not
have noticed it but the winds in a typhoon move in a certain direction. They go
around a central area. Take a look at Figure 1.
The picture shows a supertyphoon as viewed from up above the Earth. A
typhoon looks the same, only smaller. See the clouds in a spiral arrangement? They
are being blown by winds in a counter-clockwise direction. In a supertyphoon, the
wind speed is greater than 200 kilometers per hour (kph).
If the wind speed is less, from 119 to 200 kph, then it is called a typhoon. If
the wind speed is between 65 and 118 kph, it is called a tropical storm. And when
the wind speed is between 35 to 64 kph, it is a tropical depression.
Figure 1. A supertyphoon as seen from high above the
Earth; at the center is the “eye” of the supertyphoon.
Image by NASA Earth Observatory

139
Tropical depression, tropical storm, typhoon, and supertyphoon are
categories of tropical cyclones (Table 1). In simple terms, a tropical cyclone is a
system of thunderstorms that are moving around a center. As the winds intensify or
weaken, the category is upgraded or downgraded accordingly.
Table 1. Tropical Cyclone Categories
Category
Maximum Wind Speed
kilometers per hour (kph)
Tropical Depression 64
Tropical Storm 118
Typhoon 200
Supertyphoon greater than 200
The term typhoon is used only in the northwestern part of the Pacific Ocean.
In the northeastern part of the Pacific Ocean and in the northern part of the Atlantic
Ocean, the equivalent term is hurricane. Thus, a hurricane on one side of the Pacific
Ocean will be called a typhoon if it crosses into the other side.
In the Philippines, we use the same word for all categories of tropical
cyclones. We call it bagyo whether it is a tropical depression, a tropical storm or a
typhoon.
(At this point, your teacher will give a demonstration.)
Philippine Area of Responsibility
When a weather disturbance enters the Philippine Area of Responsibility
(PAR), the weather bureau begins to monitor it. Do you know where the PAR is? Do
the following activity to find out.

140
Activity 1
Plotting the PAR
Objectives:
1. read map,
2. given the latitude and longitude of a tropical cyclone, tell if it has
entered the Philippine Area of Responsibility, and
3. explain what is meant when a typhoon has entered the Philippine Area
of Responsibility.
Materials Needed:
map of the Philippines and vicinity
pencil
Procedure:
1. Plot the following points on the map below (Figure 2).
Points Latitude, Longitude
a. 5°N, 115°E
b. 15°N, 115°E
c. 21°N, 120°E
d. 25°N, 120°E
e. 25°N, 135°E
f. 5°N, 135°E

141
Figure 2. Map of the Philippines and vicinity
Mainland China
Taiwan
Borneo
PACIFIC OCEAN
115° 116° 117° 118° 119° 120° 121° 122° 123° 124° 125° 126° 127° 128° 129° 130° 131° 132° 133° 134° 135°
28°
27°
26°
25°
24°
23°
22°
21°
20°
19°
18°
17°
16°
15°
14°
13°
12°
11°
10°
9°
8°
7°
6°
5°
4°

142
2. Connect the plotted points. The region within is the Philippine Area of
Responsibility or PAR. It is the job of PAGASA to monitor all tropical cyclones
that enter this area.
Q1. If a typhoon is located at 15°N, 138°E, is it within the PAR?
Q2. How about if the typhoon is at 19°N, 117°E, is it inside the PAR?
Under What Conditions do Tropical Cyclones Form?
Shown below are the tracks (paths) of four tropical cyclones that entered the
PAR in the past years. The tracks were plotted by PAGASA. Study the maps and
answer the following questions.

143
Figure 3. Tracks (paths) of selected tropical cyclones
Where did the tropical cyclones form? On land or in the ocean?
What can you say about the temperature of the bodies of water in the vicinity
of the Philippines? Is the water warm or cold?
In what direction did the tropical cyclones move?
Which part of the Philippines was hit by the four tropical cyclones?
In the case of Agaton, Yoyong, and Huaning, where did they die out? Near
land or in the middle of the ocean?
Tropical cyclones need water vapor in order to form. Which is a better source
of water vapor, landmasses or oceans? The answer is obvious. But not all parts of
the ocean can provide water vapor. Where do you think would evaporation be
greatest, near the equator or away from the equator?
Thus, tropical cyclones require warm ocean waters to be able to develop.
According to scientists, the temperature of ocean water must be 26.5°C or greater.
Given this information, do you think typhoons can form in latitudes away from the
equator? Why or why not?

144
From the maps, you can see that tropical cyclones generally move in a
northwest direction. The reason is because there are large-scale winds that push the
tropical cyclones in that direction. This is similar to the way a whirlpool is carried
along by a flowing stream.
As you can observe, all four tropical cyclones struck the northern part of the
Philippines. Now you know why the southern part of the Philippines is often
untouched by tropical cyclones. Where do you think should a tropical cyclone form
so it would hit the Mindanao area?
Three of the tropical cyclones mentioned above weakened and died out near
land. Agaton dissipated in Luzon, Yoyong in Taiwan, and Huaning near Mainland
China. This means that when tropical cyclones reach land, they die out because they
are cut off from the warm ocean waters that keep them going.
Now you know where tropical cyclones start to form, why they form there, and
in what direction they generally move. Can you now explain why the Philippines is
prone to typhoons?
In the following activity, you will try your hand in tracking a tropical cyclone as
it enters and leaves the PAR.
Activity 2
Tracking a tropical cyclone
Objectives:
1. determine if your location is in the path of a tropical cyclone, given the
latitude and longitude position and
2. explain why PAGASA regularly monitors when a tropical cyclone is
within PAR.
Materials Needed:
map with the PAR (from Activity 1)
tracking data
pencil

145
Procedure:
1. Use the latitude and longitude (lat-long) in the table below to track the
location of Sendong. Plot each lat-long pair on the map with the PAR.
Date: 13-19 DEC 2011
Tropical Storm Sendong (International name: Washi)
Month/Day/Time Latitude (°N) Longitude (°E)
12/13/06 6.00 145.10
12/13/12 6.40 143.30
12/14/18 6.00 141.70
12/14/00 5.90 140.60
12/14/06 6.20 139.00
12/14/12 6.70 137.70
12/14/18 7.00 136.30
12/15/00 7.20 134.30
12/15/00 7.20 134.30
12/15/06 7.60 132.30
12/15/12 7.70 130.80
12/15/18 7.50 129.10
12/16/00 7.40 128.10
12/16/06 8.00 126.80
12/16/12 8.40 125.50
12/16/18 8.50 123.80
12/17/00 9.10 122.40
12/17/06 9.20 121.50
12/17/12 9.60 120.40
12/17/18 10.20 119.00
12/18/00 10.90 117.60
12/18/06 10.30 115.70
12/18/12 9.90 114.60
12/18/18 9.60 113.90
12/19/00 9.10 112.90
12/19/06 9.70 111.90
12/19/12 10.50 110.70
Tracking data are from
http://weather.unisys.com/hurricane/w_pacific/2011H/index.php

146
Q3. Where did Sendong form?
Q4. When did Sendong enter the PAR?
Q5. When did Sendong leave the PAR?
Q6. In what direction did Sendong move?
Sendong started out in the Pacific as an area of low pressure. Because it was
just a low-pressure area, it was not given a name. Then it intensified into a tropical
depression. Again it was not yet given a name because it was still outside the PAR.
When it finally entered the PAR, it had already strengthened into a tropical
storm. Since it was within the PAR by then, PAGASA gave it a name—Sendong—
from its prepared list. Internationally, the tropical storm was called Washi.
Sendong brought hours of torrential rains to Mindanao. Some places received
more than 200 mm of rain. Because of the excess rain, flash floods and landslides
took place. Nearly a thousand people were killed, many in the cities of Cagayan de
Oro and Iligan. Damage to houses, roads, and bridges reached up to 2 billion pesos.
After the Sendong disaster, who would have thought that another tropical
cyclone would again hit Mindanao the following year. Tropical cyclone Pablo
(international name, Bopha) was so strong it was categorized as a supertyphoon.
Clearly, we need to learn about tropical cyclones in order to survive.
Inside Tropical Cyclones
One thing about tropical cyclones that we should watch out for are the strong
winds. Let us now take a peek inside a tropical cyclone and find out in which part
would we experience strong winds.

147
Activity 3
Dissecting a tropical cyclone
Objectives:
1. explain what two weather factors tell weathermen that a certain location
is at the eye of a tropical cyclone; and
2. put in simple words the statement “calm before the storm.”
Materials Needed:
weather data (air pressure and wind speed)
Procedure:
1. Figure 1 consists of two illustrations. The top one shows a tropical cyclone as
seen at an angle. White rain bands move around the center or “eye”. The
bottom illustration shows a cross-section of a tropical cyclone. It is like slicing
it in half and looking at it from the side.
Figure 4. (Top) View of a tropical cyclone at an angle.
(Bottom) Cross-section of a typhoon.

148
Q7. Location A is within the eye of the tropical cyclone. B, C and D are locations
that are more and more distant from the eye. The air pressure at the different
locations are:
Location A B C D
Air pressure*
in millibars (mb)
930 960 980 990
*Air pressure refers to the weight of air over a certain area.
Compare the air pressures at A, B, C and D. What do you notice?
Q8. Location E is within the eye of the tropical cyclone. Location F is within the
clouds surrounding the eye. The clouds at F make up the eyewall. The wind
speed at the two locations are:
Location E F
Wind speed (km/hour) 10 200
Compare the wind speed within the eye and at the eyewall. What can you
say?
As you have learned from the activity, the lowest air pressure is at the eye of
a tropical cyclone. In fact, all tropical cyclones have low air pressure at the center.
This is the reason why the air in the surroundings move toward the eye. Recall in
Grade 7 that air moves toward low-pressure areas.
You also learned that at the eye of a tropical cyclone, wind speed is low. But
in the dense clouds surrounding the eye, at the eyewall itself, the wind speed is
great. When newspapers report that a tropical cyclone has sustained winds of 200
km/hour, for instance, they are referring to the winds at the eyewall.
When the eye of a tropical cyclone passes over a certain place, it is the winds
at the eyewall that wreak a lot of damage. As it approaches, one side of the eyewall
brings strong winds blowing in one direction. Then comes the eye with its somewhat
calm weather. As it leaves, the other side of the eyewall brings strong winds again,
but this time in the opposite direction.

149
Are You Prepared?
When a tropical cyclone enters the PAR and it is on its way toward land,
warning signals are issued. The following signals are used by PAGASA to warn
people about the approaching weather disturbance. Do you know what the signals
mean?
PUBLIC STORM WARNING SIGNALS (PSWS)
PSWS # 1
What it means
A tropical cyclone will affect the locality
Winds of 30-60 kph may be expected in at least 36 hours or
irregular rains may be expected within 36 hours
The following may happen
Twigs and branches of small trees are broken
Some banana plants are tilted or downed
Some houses of very light materials partially unroofed
Rice crops suffer significant damage in its flowering stage
What to do
Watch out for big waves
Listen to severe weather bulletin issued by PAGASA

150
PSWS # 2
What it means
A tropical cyclone will affect the locality
Winds of greater than 60 kph up to 100 kph may be expected in at least 24
hours
Large number of nipa and cogon houses may be partially or totally unroofed
Some old galvanized iron roof may be peeled off
Winds may bring light to moderate damage to exposed communities
Some coconut trees may be tilted while few are broken
Few big trees may be uprooted
Many banana plants may be downed
Rice and corn may be adversely affected
What to do
Avoid riding in small seacraft
Those who travel by sea and air should avoid unnecessary risks
Postpone outdoor activities of children
PSWS # 3
What it means
A tropical cyclone will affect locality
Winds of greater than 100 kph to 185 kph may be expected in at least 18
hours
Many coconut trees broken or destroyed
Almost all banana plants downed and a large number of trees uprooted
Rice and corn crops suffer heavy losses
Majority of all nipa and cogon houses uprooted or destroyed; considerable
damage to structures of light to medium construction
Widespread disruption of electrical power and communication services
Moderate to heavy damage experienced in agricultural and indistrial sectors

151
What to do
Avoid riding in any seacraft
Seek shelter in strong buildings
Evacuate from low-lying areas
Stay away from coasts and river banks
PSWS # 4
What it means
A very intense typhoon will affect locality
very strong winds of more than 185 kph maybe expected in at least 12 hours
Coconut plantation may suffer extensive damage
Many large trees maybe uprooted
Rice and corn plantation may suffer severe losses
Most residential and institutional buildings of mixed construction maybe
severely damaged
Electrical power distribution and communication services maybe severely
disrupted
Damage to affected communities ca be very heavy
What to do
All travels and outdoor activities should be cancelled
Evacuation to safer shelters should have been completed by now
The locality is very likely to be hit directly by the eye of the typhoon.
To be fully prepared for tropical cyclones, you should also put together an
emergency kit which includes the following: drinking water, canned goods, can
opener, radio, flashlight, extra batteries, clothes, blanket, and first aid kit. You never
know when you will need it. You must learn how to rely on yourself. In times of
disaster, it may take a while before help arrives.

152
Tarbuck, E.J., & Lutgens, F.K. (2004). Earth Science (10th
ed.). First Lok Yang Road,
Singapore: Pearson Education (Asia) Pte Ltd.
http://www.pagasa.dost.gov.ph/
http://www.ready.gov/hurricanes
http://www.noaawatch.gov/themes/tropical.php
http://weather.unisys.com/hurricane/w_pacific/2011H/index.php
http://en.wikipedia.org/wiki/Tropical_Storm_Washi
http://people.cas.sc.edu/carbone/modules/mods4car/tropcycl/index.html

153
COMETS, ASTEROIDS,
AND METEORS
Overview
Recent advances in space technology have allowed scientists coming from
different background such as physics, chemistry, biology, and geology to collaborate
on studying Near-Earth Objects (NEO) such as comets and asteroids. With more
powerful telescopes and space probes, the study of comets and asteroids provides
more clues about the origins of our solar system. Over the past three years, amateur
and professional astronomers have discovered several NEOs that came close to
Earth, the most recent asteroid being Asteroid 2012 DA14. It made a very close
approach to Earth as it orbited the Sun on February 16, 2012 (Philippine Time). In
the morning of the same day, an asteroid entered Earth’s atmosphere and exploded
over Lake Chebarkul in Russia hurting about 1,000 people in the process. These two
events triggered superstitions, fears, and doomsday prophecies held by different
cultures. But do these things have scientific basis?
Has Earth ever been hit by a comet or an asteroid?
If yes, how have such impacts affected Earth?
How often does a comet or an asteroid hit Earth?
Unit 2
MODULE
3

154
Activity 1
What happens when a comet or an asteroid hits
Earth?
Objectives:
1. describe how impact craters are formed when a comet or asteroid hits
Earth based on a simulation; and
2. present observations on simulating a comet or asteroid impact using
drawings.
Materials Needed:
1 rectangular container (aluminum tray or plastic)
1 pebble (1-4 cm in diameter)
colored flour/colored starch
pencil
Procedure:
1. Fill the rectangular tray with colored flour about 3-4 centimeters deep.
2. Place the tray on top of a table (or armrest of a chair).
3. Throw a pebble to hit the flour in the tray. Do this about four times, hitting
different parts of the flour in the tray.

155
4. In the space below, draw the shape of the “craters” made by the pebble on the
colored flour as:
a. viewed from the top. b. viewed from the side
5. Compare the shape of the pebble’s “crater” with the shape of the impact crater
photo shown below.
Meteor Crater near Winslow, Arizona, USA
(Permission obtained from the Center for Science Education,
UC Berkeley Space Sciences Laboratory)
Q1. What do you notice about the shape of your pebble’s crater and the shape of
the impact crater shown in the photo?
Q2. What do you think happened to the plants and animals living in the area
where the comet or asteroid crashed?
___________________________________________________________________

156
Comets and asteroids are referred to by astronomers as Near-Earth Objects
(NEO). Comets are icy bodies or objects while asteroids are rocky fragments. They
are remnants from the formation of our solar system 4.6 billion years ago. The table
below summarizes the similarities and differences between comets and asteroids.
Table 1. Comparison of some characteristics of comets and asteroids
Characteristic Comet Asteroid
Origin Kuiper Belt and Oort Cloud Main Asteroid Belt
Shape Varied/Irregular Varied/Irregular
Size range of diameter
(kilometer)
1-10 (nucleus only) 1 – 100++
Chemical composition Ice (frozen water); frozen
gases (ammonia, methane,
and carbon dioxide); other
organic compounds (Carbon-
containing compounds)
Silicates (olivine and
pyroxene), iron, nickel
Orbit Highly elliptical More rounded
Orbital period (years) 75 to 100,000++ 1-100
Q3. Which is most likely to make a more frequent “visitor” of Earth: a comet or an
asteroid? Why do you think so?
As you can see in the table, comets and asteroids have irregular shapes and
varied sizes. They both reflect light from the Sun in varying amounts depending on
the size and composition. The presence of more silicates allows a comet or asteroid
to reflect light. Silicates are minerals that contain the elements silicon, oxygen, and at
least one metal. If an asteroid has smaller amounts of silicates relative to its other
components, it would be more difficult to see it even with a telescope because only a
small area of the asteroid can reflect light thus it may appear smaller than what it
really is when viewed.
Comets and asteroids both orbit the Sun and move relatively slow when
viewed from Earth. This means, you can see a comet for up to a year in the night sky
(or even during the morning if the comet is bright enough). The major difference is
their origin or where they came from in space. Comets usually come from the Oort
Cloud which is beyond our Solar System, and a few from Kuiper Belt which is just
beyond Neptune’s orbit. Long-period comets come from the Oort Cloud, while short-
period comets come from the Kuiper Belt. Comet Halley, the most famous comet of

157
the 20th
century is the only known short-period comet. It takes 75-79 years for Comet
Halley to orbit the Sun. We see it in the sky every time it makes its nearest approach
to the Sun. All other comets that have been identified are classified as long-period
comets and takes 200 to hundred millions of years to complete their orbit around the
Sun. Asteroids, on the other hand, originate from the Main Asteroid Belt between
Mars and Jupiter. This belt is theorized by scientists to be remnants of a planet that
did not completely form.
The orbit of an asteroid is more rounded and less elliptical than the orbit of a
comet. In February 2013, Asteroid 2012 DA14 made a very close approach to Earth
as it orbited the Sun. Distance in space is measured in light years and this Asteroid
was just 0.4 light year away from Earth, the closest that any asteroid has ever been
to Earth. In December 2012, during the midst of the doomsday prophecies, Asteroid
Toutatis also made a near approach to Earth but not as close as Asteroid 2012
DA14.
Neptune
Uranus
Saturn
SUN
Kuiper Belt
Oort Cloud
Distances and sizes are not drawn to scale.

158
Another difference between a comet and an asteroid is their chemical
composition. Comets are icy objects while asteroids are rocky fragments.
Sometimes, comets may contain other elements like sodium or argon, which is
specific to a comet. Through further studies, scientists learned that Comet Hale-Bopp
contained argon which was believed to explain the very bright appearance of the
comet in 1997. Scientists also discovered a faint sodium tail, a third type of comet tail
to add to the well-known dust and plasma (or ion) tails. On the other hand, an
asteroid is mostly composed of rock (silicates) and metals (iron and nickel being the
usual metals).
The composition of a comet is important in helping scientists understand how
Earth has liquid water, which in turn made the planet livable. During Earth’s
formation, scientists theorized that the planet must have been too hot to have liquid
water on its surface. By studying comets’ orbits and the chemical composition of
materials found in impact craters found all over Earth, soil and ice samples collected
from drilling down Earth’s crust and marine layers, scientists theorized that the early
impact of comets on Earth brought liquid water to the planet.
The chemical composition of an asteroid is important in providing clues for
scientists to discover more about the chemical composition of Earth and the other
planets in the Solar System, as well as how life on Earth was affected by impacts in
the past. It is the scientists’ belief that Earth, other planets, and asteroids are
essentially similar in composition. In fact, asteroids are also called minor planets or
planetoids. Asteroids are mostly composed of metals like iron and nickel; the same
metals that are theorized to make up Earth’s core.
Permission obtained from the Center for Science Education
(CSE), UC Berkeley Space Sciences Laboratory
Comet Anatomy
Dust Tail
Coma
Nucleus
Plasma/Ion Tail

159
The discovery of high contents of iridium in oceanic sedimentary layers in
different parts of the world such as Italy, Denmark, and New Zealand during the late
1970s led geologists, Luis and Walter Alvarez to propose the Alvarez Hypothesis in
1980. Iridium is a metal belonging to the Platinum family. It is very rarely found in
Earth’s crust, but more abundant in the mantle and core. It is also abundant in our
solar system. They proposed that an asteroid with approximately 10 kilometers in
diameter made impact with Earth 65 million years ago. They thought that the impact
caused materials to be thrown up in air, thus blocking sunlight, and bringing about a
period of winter long enough to cause a mass extinction of plants and animals,
including the dinosaurs. Further, this event ended the Cretaceous Period and
ushered in the Tertiary Period.
Comets and asteroids orbit the Sun, but it is theorized by scientists that other
planets in our solar system can influence and alter the orbital path of these NEOs,
thus they come crashing towards Earth. By studying the orbits of known NEOs,
scientists have calculated the orbital periods that indicate when these objects will
make their closest approach to Earth as they orbit Sun, or predict the likelihood of a
collision with Earth. While asteroids and comets have collided with Earth in the past,
the frequency is very much longer than a human lifetime, so there is no need to
worry.
If you want to learn more about the Impact Theory, visit:
http://hoopermuseum.earthsci.carleton.ca/saleem/meteor.htm
NEAR – 433 Eros
Asteroid Eros – Permission obtained from
the CSE, UC Berkeley Space Science
Laboratory

160
Activity 2
Meteoroid, meteor, and meteorite: How are they
related?
Objectives:
1. describe the changes that happens to a fragment from a comet or
asteroid as it enters Earth’s atmosphere;
2. represent the relationship between a meteoroid, meteor, and meteorite
using a diagram; and
3. explain how meteoroid, meteor, and meteorite are related.
Procedure:
Read the selection below and answer the questions as you go along
Q1. What is a meteor?
Q2. What is a meteoroid?
Q3. What celestial (space) objects can a meteoroid come from?
Have you ever seen a shooting star
in the night sky? It appears as an
object with a tail just like a comet. It
travels quickly and appears to fall on
the ground. A shooting star is another
name for a meteor. But the truth is: a
meteor is not a star at all. A meteor is
a light phenomenon or a streak of
light that occurs when a meteoroid
burns up as it enters Earth’s
atmosphere. A meteoroid is a broken
up rock and dust from either a comet,
asteroid, the Moon, or from Mars.
Look, it’s a
shooting star!
I think it’s a
meteor.
Isn’t it a
comet?

161
Q4. What causes a meteor?
Q5. How can you differentiate a meteor from a comet when viewed from Earth?
Q6. Show where a meteoroid, meteor, and meteorite are most likely to be found
in the diagram below. Use the following symbols for each:  meteor; 
meteoroid; and  meteorite.
A meteoroid usually all burns up when it enters Earth’s atmosphere. But when a
fragment from the meteoroid survives and makes it to the ground, this space rock
fragment is now called a meteorite. So if you heard from the news on radio or
television or read from newspapers about a meteorite exploding over Russia in
February 2013, their use of the word meteorite is inaccurate. Instead, a
meteoroid exploded over Russia. The space rock fragments they collected on the
ground are the meteorites.
A meteoroid can be as small as a grain of sand or as big as a boulder. When it
enters Earth’s atmosphere, the air in front of the meteoroid heats up, causing
materials to burn up. From Earth, these glowing materials appear as a streak of
light or a fast-moving bright object that appears to have a tail just like a comet.
What differentiates the two when we see them in the sky is that a comet moves
slowly and appears in the sky for a longer time. A meteor moves swiftly and
seems to fall on the ground. It “shoots” from a point in the sky, making people
think that it is a shooting or falling star. Also, a comet is difficult to see with the
unaided eye because it is farther from Earth compared to a meteoroid entering
Earth’s atmosphere. Sometimes, a comet can be bright enough to be seen by the
unaided eye, but this is rare, such as in the case of Comet Hale-Bopp.

162
Earlier, we mentioned that a meteoroid can come from comets. Comets
orbit the Sun and leave fragments along their orbit as they continue their journey
around the Sun. These fragments continue to orbit the Sun just like their parent
comets. When Earth orbits the Sun and passes through the orbit of a comet
where these comet fragments are found, we observe many streaks of light from
Earth which is called a meteor shower. During a meteor shower, meteors seem
to originate from only one point in the sky because the meteoroids are traveling in
parallel paths with the same velocity. The meteor shower is named after the
constellation where they seem to originate from, but this does not mean that the
meteoroids come from the associated constellation. Remember: a meteor and a
meteor shower are light phenomena; they are not stars.
Outer Space
Atmosphere (Earth)
Crust
Note: Dimensions are not drawn to scale.
Q7. How are a meteor, meteoroid, and meteorite related?

163
Q8. What is a meteor shower?
Q9. Why does a meteor shower occur?
Q10. Why does it seem that meteors during a meteor shower appear to come from
only one point in the sky?
___________________________________________________________________
From the reading activity, you learned how a meteoroid, meteor, and
meteorite are related. It is a visual treat to see a meteor at night; more so if you get
to see a meteor shower. How much and how well you can see meteors in the sky
depend on several factors: air pollution; light pollution; the time of day; weather
conditions; size of the meteoroids; source of the meteoroid (comet versus asteroid);
The number of meteors that can be seen during a meteor shower vary. It
starts with the appearance of a few meteors per hour, increasing in frequency until it
reaches its peak of 1-2 meteors per minute, and then declines. The table below
shows some of the more famous annual meteor showers and the month when they
reach their peak. The dates in the peak month vary and astronomers make forecasts
of the peak days (usually lasting for three days) every year.
Table 2. Some Examples of Famous Annual Meteor Showers
Month
Source of
meteoroid
Name of the
Meteor Shower
Constellation
(where the meteor shower
seem to come from)
August Comet Swift-Tuttle Perseid Perseus
October Comet 21P/
Giacobini-Zinner
Draconid Draco
October Comet Halley Orionid Orion
November Comet Tempel-
Tuttle
Leonid Leo
November Comet Encke Taurid Taurus
December Asteroid 3200
Phaethon
Geminid Gemini
Note: There is no need to memorize the names of these comets and asteroids.
Usually, the meteoroids that cause meteor showers come from comets, but
they may also come from an asteroid like in the case of the Geminids. Earth passes
through Asteroid3200 Phaethon’s orbit where some fragments from the asteroid are
found. Once these fragments enter Earth’s atmosphere, they burn up. Meteoroids
from comets appear fuzzy because of the ice particles while those from asteroids are
clearer and distinct because they do not have these ice particles.

164
and the chemical composition of the meteoroid itself. It is harder to see them in cities
where there are many artificial light sources and where the air tend to be more
polluted causing a smog or haze to block the light coming from meteors). Meteor
showers are easier to observe at night especially between midnight up to around an
hour before dawn.
Meteorites are of importance to scientists in studying the occurrence of
different elements and compounds on Earth. This information is in turn important in
studying our mineral resources which is an important industry in any country.
Generally, there are three types: stony, stony-iron, and iron meteorites. In the
Philippines, there are only five meteorites that have been accepted internationally.
The table below enumerates these meteorites.
Table 3. Five Meteorites Found in the Philippines (Internationally Validated)
Meteorite
Year of
Discovery
Place
Discovered
Type Chemical Composition
Pampanga 1859 Pampanga Stony Iron-Nickel (7-11%); Ferrous
sulfide (FeS); Magnesium iron
silicate (olivine (Mg,Fe)2SiO4));
Calcium-Aluminum intrusions (Ca-
Al); pyroxene or XY(Si,Al)2O6 (X
can be calcium, sodium, iron+2 and
magnesium and more rarely zinc,
manganese and lithium; Y
represents smaller-sized ions like
chromium, aluminium, iron+3,
magnesium, manganese,
scandium, titanium, vanadium and
iron+2).
Paitan 1910 Paitan,
Ilocos
Stony Iron; Magnesium iron silicate
(olivine (Mg,Fe)2SiO4)); pyroxene
Calivo 1916 Western
Visayas
Stony Not yet determined
Pantar 1938 Central
Mindanao
Stony
meteorite
Iron; Magnesium iron silicate
(olivine (Mg,Fe)2SiO4)); pyroxene
Bondoc 1956 Southern
Tagalog
Stony-
iron
Metallic iron-nickel; silicates
(olivine and pyroxene)
The elements and compounds enumerated in the table show that meteorites
are very rich in mineral resources. A comet or asteroid does not only bring with it
minerals from space but also causes the Earth rocks found in these areas to change
in chemical composition. The presence of these meteorites and impact craters hold
much potential for the mining industry aside from being objects of scientific scrutiny.

165
Activity 3
Do superstitions about comets, asteroids, and
meteors have scientific basis?
Objectives:
1. provide sound, scientific evidence to support one’s stand about
superstitions on comets, asteroids, and meteors; and
2. formulate doable actions to address superstitions on comets, asteroids,
and meteors.
Materials Needed:
pen
paper (for taking notes)
Procedure
1. Research about superstitions related to comet and asteroid in the library,
internet, and by interviewing your parents or elderly neighbors.
2. Choose at least three superstitions (one from the Philippines, and the rest from
other countries).
3. Discuss each superstition with the group to answer the question: Do superstitions
about comets and asteroids have scientific basis? Why or why not?
4. List down as many scientific evidence to support the group’s answer to the
question. The group may go back to the library to research for more evidence in
books or online resources.
5. Propose doable actions that the group can do to promote a more scientific
attitude towards comets, asteroids, and meteors to their fellow students or to
family members.
TO LEARN MORE ABOUT METEOR, METEOROID, AND METEORITE, VISIT THESE LINKS:
 http://www.pibburns.com/catastro/meteors.htm
 http://hubblesite.org/reference_desk/faq/answer.php.id=22&cat=solarsystem
 http://cse.ssl.berkeley.edu/segwayed/lessons/cometstale/frame_place.html

166
-----------------------------------------------------------------------------------------------------------------
Group ______________ Date _____________________
Members ___________________________________________________________
Do superstitions about comets and asteroids have scientific basis? Why?
Answer:
___________________________________________________________________
___________________________________________________________________
Scientific facts/evidence to support the group’s answer:
Proposed actions to promote a more scientific understanding of comets, asteroids,
and meteors:

167
Celestial visitors like comets, asteroids, and meteors have always captured
the imagination of ancient civilizations. They have been thought of as bad omens or
signs of great change or challenge such as ushering disasters and wars. But with
new scientific processes and tools, as well as greater access to scientific information,
these celestial visitors have gained the appreciation and interest of many people,
scientists and non-scientists included, all over the world.
References and Links:
American Meteor Society. (2013). Meteor FAQs. Retrieved from
http://www.amsmeteors.org/meteor-showers/meteor-faq/#1
Bely, P. Y., Christian, C., & Roy, J. R. (2010). A question and answer guide to astronomy.
United Kingdom: Cambridge University Press.
Canadian Space Agency. (2004). Module 5: Comets, meteors, and asteroids. Retrieved from
http://www.asc-
csa.gc.ca/eng/educators/resources/astronomy/module5/content.asp#5
Dr. Ken Hooper Virtual Natural History Museum Ottawa-Carleton Geoscience Centre. (n.d.).
Impact theory. Retrieved from
http://hoopermuseum.earthsci.carleton.ca/saleem/meteor.htm
Jones, T. & Stofan, E. (2008). Planetology: Unlocking the secrets of the solar system.
USA: National Geographic Society.
Lawrence Hall of Science. (2013). Hands-on universe program: Cosmic cataclysms.
Retrieved from http://www.globalsystemsscience.org/studentbooks/acc/ch1
Lunar and Planetary Institute. (2012). About comets. Retrieved from
http://www.lpi.usra.edu/education/explore/comets/background/
Mihos, C. (1997-2006). Asteroids. Retrieved from http://burro.astr.cwru.edu/stu/asteroid.html
National Aeronautics and Space Administration. (2004). Asteroid 4179 Toutatis. Retrieved
from http://echo.jpl.nasa.gov/asteroids/4179_Toutatis/toutatis.html
Notkin, G. (2005-2013). Types of meteorites and classification. Retrieved from
http://geology.com/meteorites/meteorite-types-and-classification.shtml
Phillips, T. (2012). Big asteroid tumbles harmlessly pass earth. Retrieved from
http://science.nasa.gov/science-news/science-at-nasa/2012/12dec_toutatis/
To learn more about the origins of superstitions about comets, asteroids, and
meteors, visit:
http://cse.ssl.berkeley.edu/segwayed/lessons/cometstale/frame_history.html

168
Plait, P. (2002). Meteors, meteoroids, and meteorites: Oh my! The impact of meteors and
asteroids. Bad Astronomy. USA: John Wiley & Sons, Inc.
The Meteoritical Society. (2002-2012). Meteorites from the Philippines. Retrieved from
Meteoritical Bulletin Database http://www.lpi.usra.edu/meteor/metbull.php
University of California Regents. (2000). The comet’s tale: Characteristics. Retrieved from
http://cse.ssl.berkeley.edu/segwayed/lessons/cometstale/frame_characteristics.html
University of California Regents. (2000). The comet’s tale: Orbits. Retrieved from
http://cse.ssl.berkeley.edu/segwayed/lessons/cometstale/frame_orbits.html
University of California Regents. (2000). Asteroid. Retrieved from
http://cse.ssl.berkeley.edu/segwayed/lessons/cometstale/glossary/glossary_6th_new/
asteroid.html

171
THE PARTICLE NATURE
OF MATTER
Overview
In Grade 7, you recognized that there is a wide variety of materials and these
materials combine in many ways and through different processes. With this diversity
of materials, you learned that chemists came up with several ways of classifying
them—heterogeneous and homogeneous mixtures, elements and compounds,
metals and non-metals, and acids and bases. By engaging in simple scientific
investigations, you were able to recognize some properties of solutions, which are
classified as homogeneous mixtures. You also studied the properties of common
elements, compounds, metals and non-metals, as well as solutions of acids and
bases.
The approach in this module is for you to observe, experience and represent
through drawings, illustrations, or cartoons the different phenomena that will help you
gradually understand what the particle nature of matter is all about. In Activity 1, you
will use what you have learned in previous grade levels to differentiate matter from
those which are not matter. In the second and third activities, you will look at
situations that support the idea that matter is made up of tiny particles, which you
cannot observe with your unaided eyes. This fundamental idea will enable you to
learn that the properties of matter are a result of the arrangement of particles it is
made of. In Activities 4 to 6, you will use and apply the particle model of matter to
explain the following changes in matter: liquid to gas, gas to liquid, solid to liquid,
and liquid to solid. At the end of Module 1, you will be able to answer the following
key questions.
What is matter made of?
How does the particle model of matter explain some
observed properties and changes in matter?
Are solutions always liquid?
Unit 3
MODULE
1

172
Activity 1
Which is matter, which is not?
Objectives:
1. describe common properties of matter;
2. distinguish properties of matter from those of non-matter; and
3. demonstrate the skill of measuring mass.
Materials Needed:
1 teaspoon sugar in a plastic cup or small beaker
1⁄2 cup tapwater
1 piece, stone or small rock
1 piece, ball (basketball, volleyball, or small beach ball)
3 pieces of leaves (from any plant or tree)
5 small wide-mouthed bottles or cups or 150-mL or 200-mL beakers
1 platform balance or weighing scale
1 small air pump
Procedure:
Is this matter?
1. Among the materials displayed in front of you, which do you think is classified
as matter? Put a check () under the appropriate column in Table 1. You may
make a table similar to the one below. With your group mates, discuss the
reason to explain your answer for each sample. Write your answer in the last
column.
Table 1.Identifying which is matter
Sample
Is the sample
matter?
Reason for your answer
Yes No
Not
sure
sugar granules
water
stone
air inside ball
leaves
smoke
heat
light

173
2. If your group cannot agree on a common answer, you may put a check mark
under “not sure” and write all the reasons given by the members of your group.
Q1. What similarities do you observe among the firstfive given samples? Write
these common characteristics.
Q2. Does each sample have a measurable mass? Prove your answer by
demonstrating how you measure the mass of each sample. Record the mass
you got for each sample.
Q3. Do you think that each sample occupies space? Write the reason(s) for your
answer.
Q4. How about smoke? Does it have mass? Does it occupy space? Explain your
answer.
Q5. Do you think that heat and light have mass? Do they occupy space? Explain
your answer.
Based on your observations, you have just described some characteristics of
matter. As you were observing each sample of matter in Activity 1, you were focusing
on particular characteristics. These characteristics that describe a sample of matter
are called properties. Matter can have different properties. You measured the mass
of each sample of matter using a balance or a weighing scale. The mass of an
object is a measure of the amount of matter the object has. You observed that the
mass of each sample of matter in Activity 1 is different from the mass of the other
samples. You also found out that each sample of matter occupies space. The
measure of the space occupied by an object is called volume. All matter have mass
and volume. There are other properties of matter such as hardness, texture, color,
flexibility, malleability, and electrical conductivity which vary from one sample to
another.
Recall that in Grade 7, you studied other properties of matter. You performed
activities to find out some common properties of solutions. You investigated how fast
sugar and salt dissolve in water. You compared the boiling point of a substance
(distilled water) with that of a mixture (sea water).
Now that you can correctly describe matter based on the properties you have
observed, it is important that you know what matter is made of. What makes up
matter? If you hammer the stone you used in Activity 1 into much smaller pieces,
what would you get? If you turn the sugar into very fine powder, what would result?
Ice, liquid water, and steam are all the same substance, which is water, yet you can
observe that they look different from each other? How can this be explained? These
questions can be answered in the next activity.

174
Activity 2
What is matter made of?
Objectives:
1. infer from given situations or observable events what matter is made of;
and
2. explain how these observed situations or events give evidence that
matter is made up of tiny particles.
Materials Needed:
1⁄2 cup refined sugar
1 cup distilled or clean tap water
1 piece, 100-mL graduated cylinder
1 measuring cup (1 cup capacity)
1 piece transparent bottle (can hold one cup of water) or 250-mL beaker
food coloring (blue, green, or red)
1 dropper
1 stirrer (plastic coffee stirrer or stirring rod)
Procedure:
Is this matter?
1. Using a clean and dry graduated
cylinder, pour sugar until the 20 mL
mark of the graduated cylinder.
2. Transfer the measured sugar into a
250-mL beaker or transparent bottle.
3. Measure 50 mL of distilled or clean tap
water using graduated cylinder.
4. Add the 50 mL water to the sugar and mix thoroughly until all the sugar
dissolves. Taste the resulting solution. (CAUTION: Do not taste anything in the
laboratory unless specifically told to do so by your teacher)
Q1. What is the taste of the resulting mixture?

175
Q2. Think about sugar and water as made up of tiny particles. With your
groupmates, discuss and give your reason(s) for the observations you made in
Q1. You may draw illustrations to further explain your reason(s).
5. Transfer the sugar mixture into a graduated cylinder.
Q3. What is the volume of the sugar and water mixture?
Q4. Is the volume of the resulting sugar mixture equal, more than or less than
the sum (20 mL sugar + 50 mL water) of the volumes of the unmixed sugar
and water?
Q5. Think about sugar and water as made up of tiny particles. With your
6. Pour one cup of tap water into a transparent glass bottle.
7. Add one small drop of food coloring slowly along the side of the transparent
bottle.
Q6. Describe what you observe after adding the food coloring.
8. Set aside the bottle with food coloring in a locker or corner of your room without
disturbing the setup. Describe the appearance of the contents of the bottle after
one day. Compare it with the appearance when you left the bottle the previous
day.
Q7. What happens to the food coloring dropped in the bottle containing
water? Write all your observations in your notebook.
Q8. Think about food coloring and water as made up of particles. With your
__________________________________________________________________
Studying about what matter is made of involves dealing with very small
“particles” beyond what your eyes can see. In fact, the ancient Greek philosophers
proposed ideas about what matter was made of. Almost 2,500 years ago, Leucippus
and his disciple, Democritus believed that nature consisted of two things, “atoms and
the void that surrounds them” (Knieram, 1995-2013). They believed that “atoms are
physically, but not geometrically, indivisible.” For Democritus, atoms are
indestructible and completely full, so there is no empty space. Both Leucippus and
Democritus had the idea that there are many different kinds of atoms and each of
them had specific shape and size and that all atoms move randomly around in
space. However they did not give an explanation for the motion of atoms. (Knieram,
1995-2013).

176
Democritus believed that any piece of matter can be divided and subdivided
into very small particles but that this process ended at some point when a piece is
reached that could not be further divided. He called this particle, atomos, a Greek
word which means indivisible particle. Democritus’ ideas about the atom were later
challenged by other Greek philosophers, most strongly by Aristotle.
The idea of the atom was not further explored until a little over two centuries
ago when John Dalton presented concrete evidence that all matter is made of very
small particles called atoms. An atom is the smallest particle of an element that has
all the properties of the element. Today, we know that although atoms are very small,
they are not indivisible as Democritus thought, rather they consist of still smaller
particles, Democritus was right in one aspect of his belief, that is, atoms are the
smallest particles of which substances are made. In Grade 7, you learned about
elements. Atoms of most elements have the ability to combine with other atoms.
Different elements have different properties because the combining atoms are
different and the way the atoms are joined together are different. In Module 2 of this
quarter, you will learn about how the model of the atom evolved until the present
time. You will also learn that an atom is made of even smaller parts.
A molecule is a particle consisting of two or more atoms combined together
in a specific arrangement. It is an electrically neutral particle. It is the smallest
particle of an element or compound that can exist independently. For example, a
molecule of water consists of an oxygen atom combined with two hydrogen atoms.
Atoms of the same element can also combine to form a molecule. For example,
oxygen in the air consist of oxygen molecules which are made up of two oxygen
atoms.
Atoms are too small to observe. These particles cannot be seen under the
high-powered light microscopes used in school laboratories. The size of an atom is
measured in angstroms. One angstrom is a unit of length equal to one ten millionth
of a millimetre.
The best light microscope can magnify an image only about 1,500 times.
Electron microscopes create a highly magnified image of up to 1 million times. The
scanning tunneling microscope (STM) allows scientists to view and scan the surface
of very small particles like atoms. It can magnify an image 10 million times. The STM
creates a profile of the surface of an atom and then a computer-generated model or
contour map is produced. So, only a model of the surface of an atom is generated by
a computer when a scanning tunnelling microscope is used. The picture of atoms
generated is unlike the picture we take with our cameras.
In Activity 2, when you mixed sugar and water and tasted the resulting
solution, it tasted sweet because sugar is still present, though you cannot see the
sugar anymore. The volume of the mixture is less than the sum of the volumes of
the unmixed sugar and water. Why is this so? The water is made of tiny particles,
molecules, with spaces between them. Sugar is also made up of molecules bigger
than the molecules of water. The water molecules could fit in the spaces between the
sugar molecules or vise versa.

177
Figure 1(b). Blown-up image of a
portion of Figure 1a. Dots are
more conspicuous.
Figure 1(a). Continuous
image of a pointillist
painting
Photo courtesy of Maria
Laura V. Ginoy
A good analogy to consider related to matter being composed of tiny particles
is the pointillist style of painting. The images in a pointillist painting appear
continuous but if one looks closely, the images are actually made of small dots.
Pointillism is a method of painting using dots to come up with various effects. The
dots are placed singly, in rows, or randomly. These dots can also be in groups or
they can be overlapping. They can be either uniform or varied in size in the same
painting. Matter is similarly assembled, with atoms of different elements combining in
various ways to give a tremendous variety of substances.
In Figure 1(a), the image of Dolores F. Hernandez, founding Director of the
Science Education Center, now University of the Philippines National Institute for
Science and Mathematics Education Development was done through pointillist
painting. The image appears continuous. In Figure 1(b), a portion of the painting
(boxed in Figure 1a) is blown up to show that the continuous image actually consists
of dots. The lightness and darkness of the pigments give volume to the image in
order to show smoothness. Similarly, matter, which appears to be continuous like the
image in Figure 1(a) is made up of very small particles that cannot be seen with the
unaided eye.
In the next activity, you will observe a situation to infer that particles of matter
are moving and there are spaces between them.

178
Activity 3
Are the particles of matter moving? What is
between them?
Objectives:
1. infer from observations that particles of matter move; and
2. represent through a drawing/illustration what is between particles of
matter.
Materials Needed:
2 cups tap water
1 piece, 30 mL plastic syringe (without the needle)
1 piece, wide-mouthed transparent bottle (200 or 250 mL capacity)
1 piece, narrow-mouthed transparent bottle (100 mL capacity)
1 plastic or glass dinner plate
1⁄2 cup rock salt (not iodized salt) or 1⁄2 cup sand
food coloring (blue, green, or red)
Procedure:
Is
1. Pull the plunger of the syringe until it reaches the 30 mL mark of the syringe.
2. Press your thumb on the tip of the plunger and use your other thumb to push
the plunger once.
Q1. Can you push the plunger all the way through the syringe while your thumb
presses on the tip of the plunger? Why or why not?
Q2. What do you feel as you push the plunger?
3. This time, push the plunger of the syringe all the way to the end of the syringe.
Suck water from the cup or container up to the 30-mL level of the syringe.
Cover tightly the tip of the syringe with your thumb.
Q3. What do you feel as you push the plunger?
Q4. Compare what you felt when you pushed the plunger with the air and with the
water?

179
Q5. Explain what you observe. You may represent your comparison by drawing an
illustration of the syringe and the particles of air and another illustration of the
syringe and the particles of water.
4. Pour 1⁄2 cup of tap water into one transparent glass bottles.
5. Pour the 1⁄2 cup of tap water in step #4 into another bottle or beaker. Observe
carefully the flow of water.
Q6. Did water take the shape of the container?
6. This time, pour the water just on the flat surface of a dinner plate.
Q7. What do you observe? Write all your observations.
7. Examine a single piece of bottle cap. Put it inside the bottle. Observe carefully
what happens as you transfer it by tilting the bottle into the dinner plate.
Q8. What do you observe? Write all your observations.
8. Pour 1⁄2 cup of rock salt or sand into the narrow-mouthed bottle. Observe
carefully what happens to rock salt as you pour it into the bottle and when all of
it has been transferred.
Q9. Did rock salt or sand take the shape of the bottle? Did the particles of rock salt
change in shape?
Particle Models of the Three States of Matter
From Activity 3, you observed that you could slightly push the plunger of the
syringe with air in it. You felt the springiness of the air inside the syringe which gives
a hint about the distance between the particles of air. In other words, air, being a
gas, can be compressed because there are large spaces between the particles so
the particles can be made to come closer to each other. However, you were not able
to push the plunger of the syringe with water in it. You felt the resistance of the water
to being compressed. The plunger could not be pushed because water is not as
compressible as air. The particles of liquid water are closer to each other and it is
difficult to push them even closer to each other.
From the idea that matter is made up of particles and the situations that you
observed, your drawings show how you “see” matter beyond what you can observe
with your unaided eyes. You were creating your own mental picture and constructing
models, which are drawings or diagrams that are representations of what is
happening at a level beyond what your eyes can see. This is what science educators
call the sub-microscopic model of representing an idea or concept, which you
cannot observe with your senses or even aided by a simple microscope. From your
discussions, you may have also thought of ways to make your models more
consistent with the evidence you observed.

180
At this stage, it is possible that the mental models you have drawn do not
perfectly match those that you see in books. Keep in mind that the models are not
like the pictures taken by a camera. They are only representations of reality.
The particle model of matter shows that in gases, the particles move at
random directions very quickly and travel in straight-line paths. In the process, they
collide with one another and with the walls of the container. They change direction
only when they rebound from the collisions. The distance between particles is large
compared to the size of the particles. The attraction between particles is negligible
because of the large distance between them. This explains why a gas spreads. Its
particles fill all the available space in the container.
Gases take the shape of the container because the particles are able to move
freely to all parts of the container. They move freely because they are far apart and
there is negligible attraction between them. This model also explains the
compressibility of gases. The distances between particles are large and so there is
room for the particles to move closer to each other.
In liquids, the particles are closer to one another, nudging one another as
they move. Since the particles are closer to one another, the attraction between
particles is stronger than those in gases. The particles move and change positions
but not as freely as those in a gas.
As you observed in the activity liquids can flow out of a container and can be
poured into another while maintaining their volume. This happens because there are
attractions among the particles of liquid which hold them together although not in
fixed positions. These attractions also make it possible for liquids to have a definite
volume. This is one major difference between liquids and gases, the particles are
attracted to one another more strongly than the particles of gases are.
Figure 2. The particle view of a gas

181
When you poured water and rock salt in
separate containers, you observed that a liquid,
such as water flows and it spreads out and
takes the shape of the container. If you looked
closely as you poured the rock salt, the little
pieces of solid salt maintained their shape even
as the entire sample may take the shape of the
container.
Solids have definite shapes and volume
because the particles are packed closely
together in fixed positions. They vibrate a little
but in these fixed positions. The particles
cannot move around. The particles of solids are
held together by strong forces. One common
characteristic of both solids and liquids is that
the particles are in contact with their neighbors,
that is, with other particles. Thus they are
incompressible and this commonality between
solids and liquids distinguishes them from
gases.
There are other properties that you will learn in Grades 9 to 12 that will be
useful for distinguishing among the states of matter. In general, the three states of
matter differ because of the arrangement and motion of the particles in each state.
So far, based on Activities 1 to 3 and your teacher’s explanation, you learned
that matter is anything that has mass and volume and you now have a better
“picture” or view of how the particles are arranged in the three states of matter: solid,
liquid, and gas.
 Matter is made up of tiny particles.
 Particles of matter are moving all the time.
 These particles have spaces between them.
 The particles of matter attract each other.
Figure 3.The particle view of a liquid
Figure 4. The particle view of a solid

182
These ideas are some of the features of what scientists call the particle
model of matter.
In Activity 4, you will explain the changes taking place when liquid water is left
in an open and in a closed container using the particle model of matter.
Activity 4
What changes take place when water is left in an
open container? In a closed container?
Objectives:
1. describe what happens to water when it is left in an open container for
some time;
2. represent through drawings/illustrations what happens to the particles of
water when it is left in an open container;
3. describe what happens to water when it is left in a closed container for
some time; and
4. explain the processes taking place at the sub-microscopic level.
Materials Needed:
1 cup tap water
3 pieces, watch glass or 2 pieces, shallow transparent plastic container with
covers (used for condiments)
1 piece, 1 teaspoon or 1⁄2 measuring tablespoon
Procedure:
Is this matter?
1. Pour 1 teaspoon or 1⁄2 tablespoon of tap water into the watch glass. This is
container No.1. You can write “No. 1” on a piece of paper and place it under
the watch glass. Cover container No.1 and set it aside.
2. Pour 1 teaspoon or 1⁄2 tablespoon of tap water into the second watch glass.
This is container No. 2. Do not cover container No. 2.
3. Put container No. 2 beside container No. 1 in an area of your laboratory or
room where these can be kept overnight.

183
4. During your next science class, discuss with your groupmates the following
questions and write your answers in your notebook.
Q1. Describe what happened to the water in container No. 1.
Q2. Describe what happened to the water in container No. 2. Compare the volume
of water left in container Nos. 1 and 2.
Q3. Where do you think did the water go? Describe this process by writing your
description or drawing an illustration. Label the parts of your drawing. You can
use “call outs” in your drawing.
Q4. Would anything happen differently if you heated container No. 2? Explain your
answer.
Changes between a Liquid and a Gas
In Activity 4, you observed that the volume of water from an open container
decreased after leaving it overnight. In fact, nothing of the 1/2 tablespoon of water
was left on the watch glass. How do we explain this? Based on the particle model of
matter, particles are always in motion. Note that the particles mentioned in this case
are the molecules of water. These molecules have kinetic energies that differ from
each other. Some particles are moving faster than others and therefore have higher
kinetic energy and some are moving slower. So, even at room temperature, some
molecules of water have enough kinetic energy to overcome the attraction of
neighboring molecules and escape from the surface of the liquid and eventually
move into the air. To break away from the surface of the liquid, the molecules must
have at least some minimum kinetic energy. The process by which the molecules on
the surface of a liquid break away and change into gas is called evaporation.
Usually, it is described as the process where a liquid is changed into a gas.
As evaporation takes place, the water molecules which did not escape and
were left in the liquid have a lower average kinetic energy than the molecules that
escaped. The effect of this is the decrease in the temperature of the liquid water.
Evaporation is a cooling process.
You can feel this cooling effect yourself when you apply acetone on your nails
or rubbing alcohol on your arms. Acetone and rubbing alcohol are volatile liquids.
They readily evaporate. As they evaporate, the molecules get heat energy from your
body leaving you with a cool sensation.
It is important to remember that the evaporation of a liquid in a closed
container is different from evaporation from an open container. In a closed
container, no particles can escape into the air outside the cover of the container. In
Activity 4, you may have observed that droplets of water formed under the watch
glass which covered the second watch glass with water. So, evaporation still

184
happens in a covered container. Some of the molecules of water on the surface of
the liquid escape and go into the gaseous state. These molecules may then collide
with the inner surface of the cover and as more and more of these molecules do so,
some may stay on the cover, accumulate and form droplets. This process where a
gas is changed into a liquid is called condensation. It is the reverse of evaporation.
In a closed container, the molecules of water continue to evaporate and
condense, but there is no net change in the number of molecules in the liquid or in
the gas phase. Molecules of water that previously evaporated are condensing, but
other water molecules are evaporating.
There are many other examples of condensation that you may have
observed. Condensation is responsible for ground-level fog that we see on some
cold days or along the highway leading to Baguio, for your eye glasses fogging up
when you go from an air conditioned room or vehicle to the outdoors on a hot day,
and for the water that collects on the outside of your glass of cold drink.
In the next activity, you will represent your ideas through a written description,
a cartoon, or simply an illustration and explain the changes taking place when water
is heated or cooled using the particle model of matter.
Activity 5
What changes take place when water is heated or
cooled?
Objectives:
1. describe what happens to water when it is heated;
2. describe what happens to water when it is cooled;
3. represent through drawings/illustrations what happens to the particles of
water when it is heated and then cooled; and
4. explain the processes taking place at the sub-microscopic level.
Materials Needed:
100 mL tap water (or 1⁄2 cup tap water)
1 piece, beaker or Erlenmeyer flask, 200 or 250 mL
1 piece, small watch glass
1 piece, tripod

185
1 piece, wire gauze (without the asbestos)
1 piece, alcohol lamp
safety matches
1 marker pen (any color)
Procedure:
Part A. Boiling Water
Is this matter?
1. Pour 1⁄2 cup or 100 mL of water into the beaker and mark the level of water
outside the beaker.
2. Put the beaker with water on top of the tripod as shown
in Figure 5.
3. Let the water boil using the alcohol lamp. Observe
carefully what is happening to the water when it is
already boiling.
Q1. Describe what you observe in the water inside the
beaker and above the level of water.
4. You may do any of the following: write a
description or draw a cartoon or illustration to
demonstrate how the particles of water behave
as they are heated.
Add to your skit or cartoon or illustration your answers to Q2 to Q5.
Q2. What do you think is inside the bubbles that form when the water boils? Where
did they come from?
Q3. If you keep the water boiling for more than 10 minutes, what do you think will
happen to the amount of water in the beaker? Why?
Q4. Where did the water go?
Q5. Can you explain by illustration how the water changes from liquid to gas? What
is happening to the particles of water?
5. After boiling the water for 10 minutes, remove the alcohol lamp and put off the
flame.
Figure 5.Setup for boiling
water

186
Part B. Cooling Water
Is this matter?
1. Using the hot water that has boiled from Part A, cover the beaker with watch
glass.
Q6. Describe what you observe in the water inside the beaker and at the bottom of
the watch glass.
You may do any of the following: write a description or draw a cartoon or
illustration to demonstrate how the particles of water behave as they are
heated.
Add to your skit or cartoon or illustration your answers to Q6 to Q9.
Q7. Where does the water at the bottom of the watch glass come from?
Q8. Can you explain by illustration how the water changes from gas to liquid?
Q9. Describe what is happening to the particles of water.
In Part A, Activity 5, you observed that after boiling water for some time, the
amount of water inside the beaker decreased. As the water is heated and the
temperature of the water rises, the molecules gain more kinetic energy and they
move faster. More molecules therefore have the energy to overcome the forces of
attraction of the adjacent molecules. These molecules escape to the gaseous phase.
This is evaporation.
This evaporation and formation of gas can happen even below the surface of
the liquid. When this happens bubbles are formed, rise to the surface and escape
into the air. This is the bubbling phenomenon that you see when water boils.
In Part B, Activity 5 of this module, you observed that as the water began to
cool, droplets formed under the watch glass that covered the beaker containing hot
water. Where did these droplets come from? The molecules that escape from the
liquid and go into the gaseous phase is called vapor and in this case, water vapor.
The water vapor rises and some molecules touch the glass. The glass is cooler than
the boiling water so some of the heat energy of the vapor molecules are transferred
to the glass, in effect, cooling the water vapor. When a gas is cooled, the motion of
the particles slows down. If the particles lose enough energy, their attraction for each
other can overcome their motion and cause them to associate with one another to
become a liquid. This is the liquid observed under the watch glass in the above
activity. This process is called condensation.

187
Recall two aspects of the particle model of matter: particles are moving all the
time and there are forces that act between the particles. These principles can explain
at the sub-microscopic level what you observed in Part B, Activity 5. Not all of the
water changed from liquid to water vapor. There was still liquid water left in the
beaker. Some of the molecules do not have the energy to overcome the forces of
attraction of the neighboring molecules. In addition, some of the molecules of water
that escaped to the vapor phase, hit the molecules on the surface of the liquid and if
they do not have sufficient energy, the attraction of molecules on the surface cause
them to stay and join the liquid phase.
In Activity 6, you will draw a model and explain the changes taking place
when ice is changed to liquid water using the particle model of matter.
Activity 6
What changes take place when ice turns into
liquid water?
Objectives:
1. represent through drawings or cartoons what happens to the particles of
ice when it turns to liquid; and
2. explain the processes taking place using the particle model of matter.
Materials Needed:
2 pieces, ice cubes
1 piece, watch glass or saucer
Procedure:
Is this matter?
1. Put one piece of ice cube on a watch glass or small saucer.
2. Observe what happens to the ice cube after 2 minutes.
3. You may do any of the following: write a description or draw a cartoon or
illustration to show how the particles of water behave as ice changes to a
liquid.

188
Q1. Explain what is happening to the particles of water in ice as it turns to liquid
using the particle model of matter.
Q2. Explain what will happen to the liquid on the watch glass or saucer if it is
transferred into a small container and left inside the freezer after a few hours or
overnight?
Changes between a Solid and a Gas
In Activity 6, you observed that after about 15 to 20 minutes, the ice (solid
water) on the watch glass or saucer turned into liquid water. The ice cube, which was
taken from the freezer is at a lower temperature than the surrounding room
temperature. Some of the heat energy of the surroundings is transferred to the water
molecules in the ice. This increases the kinetic energy of the molecules and as the
heat transfer continues, the particles gain more and more kinetic energy. The
molecules vibrate faster and faster and at some point have enough energy to
overcome the forces that hold them in their fixed places in the solid. Since the
molecules vibrate so fast, they break away from their fixed positions. The
arrangement of the water molecules in ice gradually becomes disorganized and the
solid where the molecules are in fixed positions turns to liquid where the molecules
are more free to move. This transformation process in which a solid is changed to a
liquid is called melting.
On the other hand, when you put liquid water inside a freezer, the cooling
system of the refrigerator removes heat energy from the water molecules as a result
of which they have less kinetic energy and move more slowly. As more and more
heat is removed and as the molecules move more slowly, the forces of attraction
between the molecules cause the molecules to be aligned. As this removal of heat
continues, the molecules lose so much energy that they are not able to move from
place to place but only able to vibrate in place. In time, the liquid water becomes
solid water, which is ice. Freezing is the process in which a liquid is changed to a
solid.
Note that liquid water that freezes is still water. Similarly, ice that melts is still
water. This is why after melting an ice cube, you can freeze the liquid water back to
ice. In other words, the same molecules of water are involved when these changes
occur.

189
In Activities 1 to 6, you have learned the four basic aspects of the particle
model of matter. These are: (1) matter is made up of very small particles; (2) matter
is made up of particles that are constantly moving; (3) there is empty space between
the particles; and (4) there are forces that act between the particles. Using this
model, you were able to infer that the arrangement and motion of the particles of
matter, as well as the attraction between them change when they change from one
state to another. However, the same particles of matter are involved when these
changes happen. The particle model of matter can explain the following phase
changes: evaporation, boiling, condensation, melting, and freezing.
Annenberg Foundation (2012). Workshop session 2: The particle nature of matter:
Solids, liquids, and gases. In Essential Science for Teachers: Physical
Science. Retrieved from
http://www.learner.org/courses/essential/physicalsci/support/ps_session2.pdf
Brady, J.E., & Senese, F. (2004). Chemistry: Matter and its changes (4th
ed.). River
Street Hoboken, NJ: John Wiley & Sons, Inc.
Frank, D. V., Jones, T.G., Little, J.G., Miaoulis, B., Miller, S., & Pasachoff, J.M.
(2008) California focus on physical science. Boston, Massachusetts: Pearson
Prentice Hall.
Knierim, T. (1995-2013). Leucippus and Democritus [Abdera, 460 - 370 BC].
Retrieved from http://www.thebigview.com/greeks/democritus.html.
The ekShiksha Team, Affordable Solutions Lab (ASL), Indian Institute of Technology,
Bombay, India (n.d.). Matter in our surroundings. Retrieved from
http://www.it.iitb.ac.in/ekshiksha/eContent-Show.do?documentId=88
The NSTA Learning Center, ACS-NSTA Web Seminars.(2012, May). Matter –solids,
liquids, and gases: Introducing a free online resource for middle school
chemistry. Retrieved from
http://learningcenter.nsta.org/products/symposia_seminars/ACS/webseminar10.
aspx
The NSTA Learning Center, ACS-NSTA Web Seminars.(2012,July).Changes of
state: evaporation, condensation, freezing, and melting - Introducing a free
online resource for middle school chemistry. Retrieved from
http://learningcenter.nsta.org/products/symposia_seminars/ACS/webseminar11.
aspx

190
Whitten, K.W., Davis, R.E., Peck, M.L., Stanley, G.G. (2004). General chemistry
(7th
ed.). Belmont, California: Brooks/Cole—Thomson Learning, Inc.
Wilbraham, A.C., Staley, D. D., Matta, M.S., & Waterman, E.L. (2007). Chemistry:
Teacher’s edition for California. Boston, Massachusetts: Pearson Prentice Hall.
United Kingdom. Department for Children, Schools & Families (2008). Using models,
science study guide. Retrieved from
http://www.iteach.ac.uk/LinkClick.aspx?fileticket=wc0DUlOOxMQ%3D&tabid=10
06&mid=7745
United States Department of Education, Louisiana States. (n.d.). Particle nature of
matter activity sheet. Retrieved from
http:www.doe.state.la.us/ldc/uploads/4249.pdf

191
ATOMS: INSIDE OUT
Overview
In module 1, you learned that matter is made up of atoms which are too small
to see with the unaided eye or even with the use of the ordinary light microscope.
When the idea of the atom was conceived by the ancient Greek philosophers, they
thought the atom is indivisible, that it has no parts.
Scientists have proven, however, that the atom is composed of even smaller
particles. From experiments conducted in the latter part of the 19th
century to the
early half of the 20th
century, scientists collected evidence that atoms are composed
of three types of particles, namely, (1) protons, (2) electrons and (3) neutrons.
These components of the atom are collectively referred to as subatomic particles.
In recent years, scientists have discovered that protons and neutrons consist of even
smaller particles. There are still many things about the atom and what is inside it that
scientists are discovering. These extremely small particles are being studied using
an extremely big structure that serves as their instrument. The thick black circle in
Figure 1 is the entire scientific instrument and its circumference is precisely 26.659
kilometers and its depth is about 100 meters. To give you a better idea how big this
structure is, find from the map a place which is about 27 km from your own town.
Working in a laboratory that aims to uncover the tiniest bits of matter that make up all
that we see around us must be truly exciting! Who knows, you might join this group
of scientists and make more discoveries about the atom. Inspiring and challenging,
perhaps? To get you started, prepare yourself to turn the atoms inside out!
Unit 3
MODULE
2

192
In the earlier grades, you learned about magnets. A magnet has two ends,
two poles, the north and the south. Put the north ends of two magnets next to each
other and the magnets move apart. How about putting the two south ends next to
each other? Yes, the same observation would be made as when both north ends are
next to each other. How about when you place the north and south ends next to
each other, what will happen? They attract each other. These observations indicate
that like ends or poles repel, unlike ends or poles attract. Electric charges (or simply
charges), either positive charge or negative charge, behave similarly, that is, like
charges repel or push away each other and unlike charges attract or pull toward
each other. Keep this kind of behavior in mind, as you do the first activity.
What makes up an atom? How do these components differ from
each other? How are these components arranged inside the atom?
How is an atom different from an ion?
Figure 1. The Large Hadron Collider at the CERN complex, Geneva,
Switzerland. Photograph courtesy of CERN. Retrieved from
http://cds.cern.ch/collection/Press%20Office%20Photo%20Selection?ln=en

193
Activity 1
“Charge” it to experience!
Objectives:
1. observe that objects may attract or repel each other,
2. infer that objects may carry positive and negative charges, and
3. deduce that neutral objects contain positive and negative charges
Materials Needed:
meterstick or any meter-long stick
balloons
string
chairs or any stand for the stick
glass (from a picture frame)
cloth (flannel or silk cloth)
Procedure:
1. Inflate the two balloons. Tie each using a length of string. Place the meter-long
stick across two chairs. Suspend the two balloons so that they hang freely
about two inches apart.
2. With each hand holding one balloon, rub the balloons simultaneously against
your hair several times. Let go of the balloons. Observe.
Q1. What happened with the balloons?
Q2. Did the balloons acquire the same charge or different charges? What made
you say so?
3. Rub the piece of glass with a silk cloth. Bring the piece of glass between the
two balloons. Observe.
Q3. What happened with the balloons?
Q4. Does the glass have a different or same charge as the balloon? What made
you say so?

194
From the activity above, you have “experienced” that objects, even they seem
to be neutral, can carry “charges”. In fact, you were able to charge the objects by
rubbing them against another object; just like when you rubbed the balloons onto
your hair. You can infer that after you have rubbed the balloons, they acquired a
charge since they pushed away each other. You can even say that the balloons
acquired the same charge. They have indeed! The balloon, or synthetic rubber, the
material the balloon is made of, acquire negative charges when rubbed. Have you
experienced the same with your hair after brushing it? Did you observe some
unusual behaviour, too? Was it a “hair-raising” experience? Why do you think this
happened?
How about the rubbed glass? What charges do you think the glass carried
after it was rubbed with the cloth? Yes, the glass was positively-charged since the
negatively-charged balloons were attracted towards the glass. From here, you can
infer that objects are electrically neutral, or simply, neutral, but they carry electrical
charges.
But where do all these charges come from? In module 1, you have learned
that all matter, including the objects that you used in Activity 1, are made up of
atoms. Atoms, of which all objects are made, are electrical in nature. Atoms contain
particles with positive and negative charges. The proton carries a positive charge
(+1). The electron carries a negative charge (-1). Atoms, in their most stable state
are neutral with an equal number of protons and electrons. So, let us say an atom
has 5 electrons, how many protons does this atom have? How about if the atom has
64 protons, how many electrons does this atom have?
The other particle in atoms is the neutron which does not carry any charge or
is neutral; as you may have guessed from the name it was given. Consider an atom
which has six protons, six electrons and six neutrons, is the atom electrically neutral?
If instead the atom has six protons, six electrons and eight neutrons, is it still neutral?
Does the number of neutrons affect the charge of the atom? With the charges of the
three subatomic particles in mind, what could be the reason that among the three
subatomic particles, it was the neutron which took the longest time to be discovered?
In fact, it was detected 30 years after the electron and the proton were discovered.
The properties of the three subatomic particles are summarized in Table 2.
One of their properties is their masses. In the next activity, you will compare the
masses of the subatomic particles and ascertain which among them contributes the
most to the overall mass of an atom.

195
Table 2. Some properties of the three main subatomic particles
Activity 2
The big difference
Objectives:
1. compare the masses of the subatomic particles using different ways of
visual representation
2. infer which subatomic particle contributes to the mass of the atom
Materials Needed:
pencil/pen
crayons or colored pencils
Procedure:
1. Refer to the masses of the subatomic particles in Table 2. Arrange the
subatomic particles in increasing mass.
Q1. Which subatomic particle is the lightest?
Q2. Which subatomic particle is the heaviest?
Q3. Which subatomic particles have almost the same mass?
Subatomic
particle (symbol)
Charge Mass, grams Location in the Atom
Electrons (e-
) -1 9.109 x 10-28
Outside nucleus
Protons (p+
) +1 1.672 x 10-24
Nucleus
Neutrons (n0
) 0 1.675 x 10-24 Nucleus

196
2. Show a comparison of the masses of the three subatomic particles using a bar
graph. Refer to Figure 2 in the next page, assuming that the first bar represents
the mass of the proton; draw the bars to represent the masses of the neutron
and the electron. Take note that the masses are expressed in the -28
exponent.
3. This time, using a pie chart, show the proportion of the masses of the
subatomic particles for an atom composed of only 1 proton, 1 neutron and 1
electron.
4. A seesaw can show a comparison between two masses of an
object. A seesaw goes up and down depending on the
mass it carries on each side.
Q4. How does the mass of the neutron compare
with the mass of the proton? Using circles to
represent the particles show the comparison
by drawing a seesaw with the particles on it.
Q5. How many electrons should be placed on one side of the seesaw to balance it
if the other side has 1 proton on it, like the one shown below? Write the number
on the space provided in the illustration below.
5. Take a look again at the different visual representations you have made.
Q6. Which subatomic particle/s make/s up most of the mass of the atom?
In the activity above, you have visually compared the masses of the three
subatomic particles. You have “seen” that protons and neutrons are “massive
indeed”. Electrons are very much lighter than the protons and neutrons, to the
point that its mass does not significantly contribute to the mass of the entire atom.
In effect, the mass of the electron is negligible.
The massive part of the atom, then, comes from the masses of the protons
and neutrons. Collectively, the protons and neutrons are called nucleons. The
nucleons, tightly packed together, form the nucleus in the center of the atom.
Thus, most of the mass of the atom is contained in its nucleus. In the succeeding
activities, you will learn more about the nucleus and how it was discovered.
_____ e-
1p+

197
16720
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
proton neutron electron
mass(x10-28grams)
Figure 2. Masses (expressed in x10-28 grams) of the subatomic particles

198
Activity 3
Small but terrible
Objectives:
1. simulate and describe Thomson’s model of the atom
2. simulate and describe Rutherford’s model of the atom
3. deduce that scientific models may change over time
Part A
Materials Needed:
Box containing a marble and a regularly shaped object fixed in place
Procedure:
1. Get the activity box from your teacher. Write the box number on your
worksheet. Inside the box are the “mystery object” which is fixed in place and
one marble. Without opening the box, guess the shape, size and location of the
mystery object.
Q1. What is the shape of your “mystery object”?
Q2. What is the size of the “mystery object”? Draw a picture of the “mystery object”
showing its size relative to the box.
Q3. Where is it located in the box? Draw a picture of the “mystery object” showing
its location within the box.
Q4. How were you able to infer the shape, size and location of the “mystery object”
in the box?
2. Open the box and check how close you are in guessing the size, shape and
location of the “mystery object”.
Q5. How close was your guess? If given the chance to guess another “mystery
object”, will you change your strategy? If yes, what changes will these be?
3. With the permission from your teacher, you may again try to guess another
“mystery object”.

199
How was your experience in Part A? Perhaps, you had felt the same
excitement as what our scientists felt when they are trying to determine what was
inside the atom, its structure. The excitement comes from guessing about something
that is unseen, much like guessing what is inside a box that you received as gift on
your birthday! The scientists had to look for ways to find out what the eyes cannot
see, similar with what you did in Part A.
When the idea of the atom was first proposed by the ancient Greeks, they
thought it was a particle with no parts. However, towards the 19th
century, J.J.
Thomson was able to discover that atoms have negatively-charged particles, which
he called electrons. It led him to propose a new model for the atom, which he called
the plum pudding model. Thomson proposed that the negatively-charged electrons
were embedded in a kind of
cloud or soup of positive charge,
as shown in the figure on the
right. Since plums and puddings
are not commonly known in the
Philippines, it may work better
for you that we use the other
name for the model, the raisin
bread model.
In science, models,
based on observations from
experiments are tested further, sometimes by other scientists, to determine their
validity. A group of scientists composed of Ernest Rutherford, Johannes "Hans"
Wilhelm Geiger and Ernest Marsden tested Thomson’s model by bombarding a very
thin sheet of gold foil with positively-charged alpha particles. Their experiment is
referred to as the alpha particle scattering experiment. In the next parts of the
activity, you will simulate parts of the experiment that the group of Rutherford did.
Part B
Materials Needed:
one piece of 25 centavo coin
paper, any small piece will do
smooth, clean table, counter or floor

200
Procedure:
1. Tear 20, very small pieces of paper, the size of mongo beans.
2. Scatter the pieces in a circle on the floor, about one foot in diameter. Imagine
these to be the electrons in the Thomson’s raisin bread model of the atom.
3. As forcefully as you can, slide the coin to hit the circle of paper pieces. Imagine
the coin to be the high speed alpha particle in Rutherford’s experiment.
Q1. What do you observe? What happened to the coin?
4. If you repeat what you did with the coin and the paper pieces many times, do
you think you will make the same observation as you did above about what
happens to the coin?
Using a setup similar to the figure below, Rutherford and his coworkers
expected all of the alpha particles to travel undeflected through the atoms of gold like
the coin in the above activity. They observed that most of the alpha particles did go
through the gold foil undeflected. But what surprised them was that there were a few
alpha (α) particles that practically bounced back towards the source and some that
were deflected at smaller angles. Rutherford was reported to have exclaimed, “It was
as if you fired a 15-inch shell at a sheet of tissue paper and it came back to hit you.”
Recall what happened in Part A. How did you manage to know some
information about the mystery object? Perhaps, you guessed by the way the marble
is “bumping” the mystery object. You may even had a guess on where the mystery
object is possibly located within the box. Perhaps, this guess also came from the
“non-bumping” of the marble to anything except the sides of the box. Similarly, the
way the alpha particles “bumped”, or did not “bump”, the particles in the atoms of the

201
gold foil led Rutherford’s team to propose another model for the atom, the nuclear
model. In the raisin bread model, where the electrons with very small mass were
scattered in a cloud of positive charge, there was no region within the atom where
there would be an appreciable net concentration of charge that would cause the
alpha particles to be deflected. To account for the few deflections and the rare
occasions of very large deflections, Rutherford, in 1911, suggested a different
structure of the atom where all the positive charge and nearly all the mass of the
atom were concentrated in a very tiny region called the nucleus at the center of the
atom. The rest of the atom, where the tiny electrons with very small mass moved,
was largely empty space through which the alpha particles could travel undeflected.
This model replaced the one proposed by Thomson and is the model that we
hold to this time, with respect to the placement of the nucleus in the atom. In Part C,
you will simulate the alpha particle scattering by the gold foil in Rutherford’s
experiment using his model of the atom.
Part C
Material Needed:
pencil
Procedure:
1. Refer to Figure 3 in the next page. Using this schematic representation of the
atoms of the gold foil, draw the path of the positively-charged alpha particles as
they move through the atoms.
Q1. What happens to a positively-charged alpha particle that comes near the
positively-charged nucleus?
Q2. What happens when the positively-charged alpha particle directly hits the
positively-charged nucleus?
2. The representation of the gold foil that has been given to you is not quite to
scale. The nucleus is very tiny compared to the size of the atom. The ratio of
the size of the nucleus to that of the atom is 1:100,000. If the nucleus were
about 1 mm in diameter, the atom would have a diameter of 100 meters, which
is about the height of 30-story building.
Q3. Imagining this relative size of the nucleus compared to the atom, would there
be many more or fewer alpha particles that would pass through the gold foil
undeflected compared to the number in your schematic representation?
Q4. What do you think are the chances of the alpha particle directly hitting the
nucleus?

202
Figure 3. Schematic representation of the atoms of a gold foil
Gold foil

203
The nuclear model of the atom proposed by Rutherford in 1912 is still the
picture of the atom that we hold today. Observations made afterward in experiments
concerning the atom support the model.
The other puzzle about the atom concerns the electrons. Imagine again the
atom as 100 meters in diameter, the nucleus, around one millimetre in diameter at
the center and the electrons are in this vast space around the nucleus. Where in this
vast space are the electrons? Are they moving? How do they move? How fast do
they move?
One of the models of the electrons in atoms is the planetary model where the
electrons were thought to move in orbits around the nucleus similar to the way
planets like the earth move around the sun. This has since been found to be
incorrect. The behaviour of electrons in the space around the nucleus is not simple to
describe. What we do know, however, are the following: (1) The electron although it
is negatively charged does not collapse into the positively charged nucleus; (2)
There is attraction between the nucleus and the electron, evidence of which is that
energy is required to remove an electron from the atom.
Notwithstanding the complex behaviour of electrons in atoms, we continue to
use a model of electronic structure (or the way electrons are “arranged” in the atom)
to help us understand and study the way atoms combine to form the millions of
compounds discovered to date.
So far, you have learned about the three subatomic particles — protons,
electrons and neutrons — and how they are arranged in the currently accepted
model of the atom. Among these subatomic particles, it is the number of protons that
identify the atoms of an element. All atoms of an element contain the same number
of protons in their nuclei. This number is the element’s atomic number. In the next
activity, you will refer to the periodic table in determining the atomic number. Notice
that no two elements have the same atomic number.
Activity 4
What’s in a number?
Objectives:
1. locate the atomic number in a periodic table,
2. identify the subatomic particles associated with mass number,
3. determine the number of neutrons from the mass number,

204
4. define an isotope,
5. interpret shorthand notations for isotopes and atoms,
6. infer that ions are formed from the removal or addition of electron/s,
7. evaluate the overall electrical charge of an atom, and
8. make an inventory of subatomic particles of a given element.
Materials Needed:
paper
pen/pencil
Periodic Table
Procedure:
1. Refer to the periodic table at the end of this module. Locate the atomic
number.
Q1. What is the element with an atomic number of 15?
Q2. How many protons does the atom of this element have?
Q3. How many protons are there in an atom of aluminum?
Q4. Which element has the smallest number of protons in its atom?
2. While the number of protons is the same with atoms of a particular element, the
number of neutrons may vary. Atoms having the same number of protons but
different number of neutrons are referred as isotopes. The isotopes are
identified through their mass number which is the sum of the number of
protons and the number of neutrons in an atom. A shorthand notation for
isotope includes the element’s symbol and mass number, for instance, Ca-40.
Consider two isotopes of carbon, C-12 and C-13.
Q5. How many protons are there in the C-12 isotope? How about the number of
neutrons?
Q6. How many protons are there in the C-13 isotope? How about the number of
neutrons?
3. Atomic mass is the mass of an atom of a particular element. It is the average of
the mass numbers of the naturally occurring isotopes of the element multiplied
with their respective abundance. You will not compute for atomic mass.
However, you have to know, at least, where to find it in the periodic table.
Refer to the periodic table at the end of this module.
Q7. What is the atomic mass of magnesium (Mg)? How about for potassium (K)?

205
4. The figure on the right shows another shorthand notation.
Information on the subatomic particles may be derived
from this shorthand. The base is the element’s symbol.
The left subscript denotes the atomic number, therefore
the number of protons may be known. The superscript at
the left denotes the mass number wherein the number of
neutrons may be derived. On the other hand, the superscript at the right
denotes the charge wherein the number of electrons may be determined. When
there is no superscript at the right, it means that the charge is zero (0).
Atoms may gain charges, as you have experienced in Activity 1. This happens
when electrons are lost or gained by the atom. When this happens, the atom
become an ion.
Consider the lithium ion shown in the notation above.
Q8. How many protons are there in the lithium ion?
Q9. How many neutrons are there in this lithium ion?
Q10. How many electrons are there in the lithium ion?
5. Complete the table below.
Isotope Element Name # of p+
# of e-
# of n0
Charge
B-6 Boron 5 1 0
N-14 Nitrogen 7 0
Fluorine 9 10 -1
Neon 10 10
Mg-24 12 10
Al-27 +3
Si-28 14
S-32 0
K-35 +1
6. Using any reference, write the shorthand notation showing mass number and
atomic number for all the naturally occurring isotopes of iron.
In the next module, you will learn more about the atomic structure in relation
to the periodic table. You will notice that a pattern emerges from the way the atoms
are arranged in the table. Hopefully, this module sparked your interest and you are
excited to know more about the atom.
Li3
7 +1

206
PERIODIC TABLE
atomicmass (gram/mol)
*newly named elements, as of June 2011. For more information, please access http://iupac.org/publications/pac/83/7/1485/

208
References
Brady, J.E., & Senese, F. (2004). Chemistry: Matter and its changes (4th
ed.). River
Street Hoboken, NJ: John Wiley & Sons, Inc.
Bucat, R.B. (Ed.). (1984). Elements of chemistry: Earth, air, fire and water, Vol. 2.
Canberra City, A.C.T., Australia.
Elvins, C., Jones, D., Lukins, N., Miskin, J., Ross, B., & Sanders, R. (1990).
Chemistry one: Materials, chemistry in everyday life. Port Melbourne, Australia:
Heinemann Educational Australia.
Hill, J.W. & Kolb, D.K. (1998). Chemistry for changing times (8th
ed.).Upper Saddle
River, NJ: Prentice Hall.
Philippines. Department of Education. (2004). Chemistry: Science and
technology textbook for 3rd
year. (Revised ed.). Quezon City: Author.
Silberberg, M.S. (2007). Principles of General Chemistry. McGraw-Hill: New York
Link
Interactive simulations. (n.d.). Retrieved from http://phet.colorado.edu/

209
PERIODIC TABLE OF
ELEMENTS
Overview
Scientists have always searched for patterns, regularities and symmetries in
nature. If a pattern can be discovered, information and data can be arranged and
organized in ways that will make it more understandable, meaningful, and useful. An
excellent example of this is the periodic table. In Grade 7, you learned about the
periodic table. The elements, the building blocks of matter, are listed in that table. In
Module 2, you learned that the atoms that make up these elements are identified by
their atomic number. In this module, you will learn that elements were arranged in
the periodic table in rows and columns according to increasing atomic numbers. This
arrangement was based on properties of elements which were found to be repeated
regularly through the elements arranged according to increasing atomic number. The
properties were recurring periodically, hence, patterns in the properties are
observed. You will recognize this incredible feature of the periodic table in this
module, as you explore its full potential as a source of information about the
elements. You might even find it like a road map as you journey in your chemistry
class. It would be helpful to keep it handy all the time.
How did the Periodic Table develop?
What information about elements can be obtained from
this organizing tool?
Unit 3
MODULE
3

210
The periodic table was developed as a result of years of painstaking work by
different scientists. Its present form was a result of meticulous and thorough study by
scientists. The first activity provides you an experience similar to those of the early
scientists who developed the periodic table.
Activity 1
Tracking the path and constructing
the periodic table
Objectives:
1. trace the development of the periodic table; and
2. describe how the elements are arranged in the periodic table.
Materials Needed:
paper
whole manila paper
pencils or pens
ruler
masking or adhesive tapes
element cards provided by the teacher (3 cm x 5 cm)
Procedure:
Part A
1. Element cards are posted on the board. The element’s properties and the
compounds it can form are listed in each card. As a class, go over each card.
Notice that the cards are arranged in increasing atomic mass. While keeping
the order of increasing atomic mass, put the elements with similar properties in
the same column.
Q1. How many groups of elements were formed?
Q2. What criteria did you use to choose which group an element belongs to?
Q3. Are there any exception/s to these trends? If so, which elements break the
trend? Why did your group arrange these elements the way you did?

211
Q4. Are there any gaps in your arrangement? Where are they? What do you think
these gaps might mean?
The development of the Periodic table could be traced back in 1817 to the
work of Johann Dobereiner, a German chemist who formed the triads of elements
with similar properties like the triad of calcium, barium and strontium. In 1863, John
Newlands, an English chemist proposed the Law of Octaves. He based his
classification of elements on the fact that similar properties could be noted for every
eight element when they are arranged in order of increasing atomic masses. Around
1869 two scientists determined a way to put the
elements in order. Lothar Meyer and Dmitri
Mendeleev both came up with periodic tables
that showed how elements should be grouped.
It is interesting to note that these two scientists
did not personally know each other, yet they
came up with the same conclusions. Both
scientists were teachers living and working in
different places. Meyer lived and worked in
Germany while Mendeleev in Russia. Both
arranged the elements in order of increasing
atomic mass while putting in groups those with
similar properties. Both of them also left blank spaces in their tables, believing that
these spaces would be filled later with elements yet to be discovered.
Part B
1. Using the table of elements you have created in Part A, place in that table the
additional element cards that your teacher will give you.
Q5. How did your table of elements change each time you added new elements?
Q6. How is the table of elements you prepared similar to the modern periodic table?
How is it different?
Q7. How do you explain the fact that tellurium comes before iodine in the modern
periodic table, though it has a higher atomic mass than iodine?
Q8. Mendeleev predicted the existence of gallium and germanium because of the
gaps in his table. Why do you think Mendeleev did not predict the existence of
the noble gases?
Q9. Refer to the modern periodic table. Suppose 2 new elements were discovered
with the atomic numbers 120 and 121. Where in the Periodic table do you think
you would place these new elements?
Q10. Suppose a new element X is known. It forms a compound with chlorine, and
the formula of this compound is XCl4. What group or family do you think this
element would belong?
Dmitri
Mendeleev
Lothar
Meyer

212
In the activity above, you had the experience of how the organization of the
elements in one table was truly a herculean task. As more information was gathered
about existing and newly discovered elements, irregularities were observed. Some
newly identified elements had properties that did not match those of the groups
already included in the periodic table. To fit into the right groups, the positions of a
few elements had to be rearranged. There were even elements that had to be placed
in the table as a new group. The table was thus revised.
Later, in 1914, Henry Moseley, an English physicist observed that the order
of the X-ray frequencies emitted by elements follows the ordering of the elements by
atomic number. This observation led to the development of the modern periodic law
which states that the properties of elements vary periodically with atomic number.
Recall what you learned in Module 2 that atomic number is equal to the number of
protons in the nucleus of an atom. The atomic number is a common characteristic of
all atoms of an element.
The modern periodic table organizes elements in such a way that information
about the elements and their compounds are easily revealed. The vertical columns of
the periodic table, called groups, identify the principal families of elements. Some
families have their
special names.
Refer to the figure
on the right, Group 1
is named as the
alkali metals, Group
2 as the alkaline
earth metals, Group
17 as the halogens
and Group 18 as the
noble gases. Groups
13 to 16 are named
based on the first
element found in
their families. Thus
Group 16 is called
the Oxygen Group.
The horizontal rows
or periods are
numbered from the top to bottom. For example, the elements lithium (Li) across neon
(Ne) form Period 2.There are 7 horizontal rows or periods in the periodic table.
The elements are grouped into blocks or series in the periodic table. In the
later grades, you will learn how elements were grouped in blocks. Refer to the figure
above, Group 3 to Group 12 constitutes one block wherein elements in this block are
referred as the transition elements. The lanthanides and actinides are special
series of elements but are also part of the transition block; they are also called the
inner transition elements. Elements from the taller columns (groups 1, 2, and 13

213
through 18) are called the representative elements or main groups of the periodic
table.
This arrangement allows us to study systematically the way properties vary
with the element’s position in the table. Similarities and differences among the
elements are easier to understand and remember.
Recall what you
learned in Grade 7. We
can use the periodic
table to identify the
known elements as
metals, nonmetals, and
semimetals or
metalloids, as shown in
the figure on the right.
A stair step line
separates metals and
nonmetals.The majority
of the elements on the
left side of the table are metals. The nonmetals are confined to the right side of the
table. Moreover, you have learned in Grade 7 that the elements along the stair step
line are the semimetals. Semimetals have the appearance and some properties of a
metal but behave like a nonmetal in certain instances. The seven elements
commonly regarded as semimetals are boron, silicon, germanium, arsenic, antimony,
tellurium, and polonium. Boron, although not resembling a metal in appearance, is
included because it resembles silicon. Silicon, germanium, and antimony, act as
semiconductors, which are important in solid-state electronic circuits.
Semiconductors are insulators at lower temperatures, but become conductors at
higher temperatures.
The physical properties of metals include luster, malleability, ductility, and
conductivity. Metals vary in reactivity. The most reactive metals will react even with
cold water while the least will not react even with acid. The ease and speed with
which a metal reacts with another substance is called its reactivity.
The reactivity of metals can cause deterioration of materials. The gradual
wearing away of a metal due to interaction with other substances is called
corrosion. In Grade 7, you have seen what happens to metals when exposed to
acids. You have seen that iron corrodes when exposed to commercial acetic acid (or
vinegar) for a long period of time. In the next activity, you will observe more of this
type of reaction using a stronger acid this time. Bear in mind that some acids such as
hydrochloric acid (or muriatic acid) which you will use in this activity can cause
serious burns. Be responsible and handle it safely. Moreover, you will notice that the
reactivity of some commonly used metals with an acid differ among metals. This
reaction also causes harmful effects. Find out practical methods to prevent this
damaging type of reaction.

214
TAKE
CARE!
Muriatic acid is
corrosive to skin. If
any acid accidentally
spills on you, wash
the affected area
with tap water.
Notify your teacher.
Activity 2
Metal… Metal: How reactive are you?
Objectives:
1. compare the relative reactivity of metals in acid solution
2. find ways of preventing corrosion due to the reactivity of metals
Materials Needed:
a piece of copper wire - 4 cm. long
a strip of aluminum – 4 x 1 cm. (Don’t use the glossy aluminum)
a strip of zinc metal – 4 x 1 cm.
an iron nail – 1 inch long
40 mL (10 – 12 % HCl) commercially sold muriatic acid
4 clean glass bottles of the same size (gerber or sandwich spread bottles will do)
10 mL glass graduated cylinder
sand paper or steel wool
Procedure:
1. Get 4 clean glass bottles
and using 10 mL
graduated cylinder,
pour 10 mL of
muriatic acid into
each bottle.
2. Prepare the iron nail,
copper wire, strips of
aluminum and zinc metals. Clean these metal samples by rubbing them with
sand paper or steel wool.
3. Place the iron nail in one glass bottle containing muriatic acid (HCl) and
observe.
4. Place a white sheet of paper behind the bottle. This will make it easier to
observe any reaction to happen.
5. Observe for 3 minutes. Record all observed changes in the table below.

215
Table 1. Data for Activity 2
Metal
Observable Reactions with Muriatic Acid
(Check and describe the metal observed )
Violent Slow No Reaction
iron
copper
aluminum
zinc
6. Repeat procedure numbers 3 to 5 using each of the remaining metals.
Compare the results.
Q1. Which of these metals – Fe, Cu, Al and Zn – reacts with muriatic acid?
Which did not react with muriatic acid?
7. Arrange the metals in the order of their decreasing reactivity.
8. A reaction does not always happen between a metal and a compound. In this
case, the reaction of metals with acid, like HCl, produces bubbles of hydrogen
and a colorless solution of the metal chloride. There is an existing definite order
of reactivity existing among metals and hydrogen according to their ability to
displace one another. This arrangement is called the metal reactivity series or
activity series of metals. The activity series is an arrangement of metals
according to decreasing order of reactivity, as shown below.
Table 2. The Activity Series of Metals
Element Symbol Group No.
Potassium K 1 Most reactive
Sodium Na 1
Lithium Li 1
Calcium Ca 2
Magnesium Mg 2
Aluminum Al 3
Zinc Zn Transition metal Decreasing
Iron Fe Transition metal chemical
Tin Sn 4 reactivity
Lead Pb 4
[Hydrogen] H Non-metal
Copper Cu Transition metal
Silver Ag Transition metal
Gold Au Transition metal
Platinum Pt Transition metal Least reactive

216
Q2. What is the position (with respect to hydrogen) in the activity series of the
metals that reacted or unreacted with muriatic acid (HCl) in the activity?
9. Locate the positions in the periodic table of the following elements from the
activity series (these are members of the representative block): potassium (K),
sodium (Na), lithium (Li), calcium (Ca), magnesium (Mg), and aluminum (Al).
Q3. Potassium, sodium, lithium are metals belonging to Group 1. In this group, how
does reactivity vary – increasing or decreasing from top to bottom in the
periodic table?
Q4. Does the relative reactivity of calcium and magnesium follow this trend?
Q5. Sodium, magnesium and aluminum belong to Period 2. Does reactivity
increase or decrease from left to right among elements in a period.
10. From your answer in Q3-Q5, make a generalization of the variation of the
reactivity of metals for those belonging to a group and for those belonging to a
period.
11. Refer to the table, Activity Series of Metals.
Q6. Which will be more reactive in the following pairs of metal in every case?
a. Mg or Na with HCl
b. Ag or Al with HCl
c. Fe or Zn with CuSO4
12. Think about the changes that you have observed around you, particularly those
involving metals. You may also try to recall what you have done in Grade 7
when you placed an iron nail in a container of acetic acid.
Q7. What harmful change/s is/are brought about when a metal reacts or mixes with
acids?
Q8. What are some ways of preventing corrosion of metals?
In the activity above, you have learned that the metals react differently with
other substances. However, a general trend emerges as seen in the Activity Series,
and evident in the periodic table as well. Refer to the periodic table, you will notice
that the reactions get more vigorous as you go down the group and tend to decrease
across a period. Therefore, with the help of the periodic table you may be able to
predict the reactivities of metals.

217
With respect to position in the periodic
table of the representative elements, metallic
character increases from top to bottom and
decreases from left to right; while nonmetallic
character decreases from top to bottom and
increases from left to right, as seen in the figure
on the right.
Metallic property relates to how easy it is for an atom to lose an electron. On
the other hand, nonmetallic property relates to how easy it is for an atom to gain an
electron. Why do metals tend to lose electrons while nonmetals tend to gain
electrons? In Module 2, you learned that the behavior of electrons is complicated to
describe. However, we use a model of electronic structure which presents a picture
where electrons occupy regions around the nucleus called electron shells. These
are also called energy levels because each electron shell corresponds to a
particular energy. Each electron shell can hold only a certain number of electrons.
The way the electrons of an atom are distributed in the various energy levels or
electron shells is called electronic configuration.
The lowest energy level is the one nearest to the nucleus. This is the energy
level that electrons occupy first. It can accommodate a maximum of 2 electrons. If
there are more than 2 electrons, they occupy the succeeding higher energy levels.
The highest energy level that an electron occupies is referred to as the outermost
shell or valence shell. The electrons in the valence shells are called valence
electrons. These electrons are the ones involved in chemical reactions. The
chemical properties of an element depend on the number of valence electrons.
The reactivity of metals is related to the ease with which they lose electrons
in their valence shell. In Module 2 you learned that when an atom loses electrons, a
cation is formed. In the next grade level, you will learn that some nonmetals, on the
other hand, tend to gain electrons thus forming anions. The formation of ions among
the elements results in the formation of many different compounds. In later levels,
you will learn that some elements, instead of losing or gaining electrons, tend to
share electrons with other atoms to form compounds. In all cases, it is the valence
electrons which participate in the formation of these compounds.

218
PERIODIC TABLE
atomicmass (gram/mol)
*newly named elements, as of June 2011. For more information, please access http://iupac.org/publications/pac/83/7/1485/

220
References
Elvins, C., Jones, D., Lukins, N., Miskin, J., Ross, B., & Sanders, R. (1991).
Chemistry one: Materials, chemistry in everyday life. Port Melbourne, Australia:
Heinemann Educational Australia.
Philippines. Department of Education, Culture and Sports.(1991). Science and
technology textbook for 3rd
year. (1st
ed.). IMC, Quezon City.
Mendoza, E.E. &Religioso, T.F. (1997). Chemistry.Phoenix Publishing House, Inc.
Quezon City.
The American Chemical Society (1988). Chemistry in the community.Kendall/Hunt
Publishing Company. Dubuque, Iowa.
Links
2008 Chemical Heritage Foundation. Retrieved from
http://www.gofoster.com/downloads/twe/chap06.pdf.
http://www.google.com.ph/search?q=Mark+Buchanan+Periodic+Table

221
UNIT 4
Living Things and Their
Environment

223
BIODIVERSITY
Overview
From Grades 3 to 7 you have studied some of the different organisms and
their easily observable characteristics. You learned about those organisms that you
find just around you and other places in the country. You were taught that organisms
form the biotic component of an ecosystem. You were introduced to the cells that
differ in plants and animals. In addition, you learned about organisms other than
plants and animals. Some of these consist only of a single cell while others have
many. You may also had a chance to look at organisms that are so small and can be
seen only with the microscope.
This module will introduce you to the concept of biodiversity, specifically the
variety of organisms living on Earth. This will discuss how they are classified and
named. It will also show the similarities and differences of these organisms. It will
describe the different groups to which these organisms belong. It will let you discover
uses of some not just as food but also in medicine, agriculture, industries and the
ecosystems where they are present. In addition, you will know about the harmful
effects of some to other organisms.
The module will further show you the advantages of high biodiversity over low
biodiversity. It will also help you recognize the value of biodiversity in your
community. Most importantly, this hopes to encourage you to start or continue
protecting and conserving your community’s biodiversity for future generations.
Unit 4
MODULE
1

224
Levels of Biodiversity
Biodiversity is coined from the words, biological diversity. Usually, scientists
would refer to three levels of biodiversity namely: different kinds of organisms
(species diversity), genetic information that organisms contain (genetic diversity)
and different kinds of places where organisms live and the interconnections that bind
these organisms together (ecosystem diversity). If you recall, you have learned
about ecosystem diversity in the lower grades. You will know more about genetic
diversity in Grade 9.
Species diversity consists of the large number and all different kinds, shapes,
colors and sizes of organisms that inhabit the Earth. It includes the smallest and the
simplest bacterium (pl. bacteria) to the complex, bigger, brightly colored flower or
fish. Add to this the carabao, the tallest acacia, the biggest elephant and a human
like you. These organisms are found in various places from the soil, to the rivers,
oceans, forests, salty or hot places, in short in every corner of the Earth. Some of
them even live in your body. At present, more than a million organisms have been
identified and named while many more are being discovered every year. Just
recently, foreign and local researchers have found that diversity of reptiles and
amphibians in the Northern Philippines is even greater than what has been known
and identified.
If there are a lot more of the organisms in the world than you can count, how
will you be able to know about them? Does an organism you see in your place, for
example, have the same name in another place? Do organisms have to be
classified? Why? Try the following activity.
Why is biodiversity important?
What human activities destroy or endanger the existence of rare
and economically important species?
What human activities help protect and conserve rare and
economically important species?

225
Activity 1
What’s in a name?
Objectives:
1. give the names of organisms as they are known in your community
2. recognize the need to have a system of classifying and
naming organisms.
Materials Needed:
pictures of organisms
pencil or ballpen
sheet of paper
Procedure:
1. Get pictures of organisms from your teacher.
2. With your group, discuss how each of these organisms is called in your
community. Accept any name which your groupmates will give for an organism.
If you know other names by which an organism is called in another place,
include them. Write these on the sheet of paper.
3. Be ready when your teacher asks you to present your work to the class. Take
note of how the other groups named each of the organisms shown.
Q1. Are there organisms that others gave the same name to as your group did?
Give examples.
Q2. Are there organisms that others gave a different name to as your group did?
What are these organisms?
Q3. What can you say about your knowledge of the organisms before the other
groups’ presentations and the teacher’s discussion?

226
Classifying and Naming Organisms
For organisms to be studied and information about them shared to those who
need it, scientists grouped them into meaningful classifications. The different groups
are ranked from the largest to the smallest groups. Large groups include many
organisms with few similarities. Small groups include few organisms having more
similarities. Organisms which have more similarities would then, be closely related
than those which have less similarities. These classifications or categories consist of
the domain, kingdom, phylum, class, order, family, genus and species.
The domain is the largest category into which organisms have been
classified. This is followed by the kingdom category subdivided into various phyla
(sing. phylum). A phylum consists of different classes, each class with several
orders, an order with different families. Families consist of several genera (sing.
genus) and each genus comprise the smallest group of various species.
A species is a group of similar organisms and capable of reproducing their
own kind. This means only members of the same species can mate and produce
fertile offspring. The dog, waling-waling (an orchid), milkfish (local name, bangus),
rice plant and humans like you are examples of a species.
With the information available about organisms from the early studies to the
present, scientists came up with the three-domain system of classification. Before,
organisms were only grouped into eukaryotes and prokaryotes. Remember in your
previous year, you knew about the nucleus in cells that contain DNA in chromosomes
having a role in heredity. In eukaryotes, these materials are enclosed in a membrane
while in prokaryotes they are not. Most prokaryotes are tiny and unicellular, thus, are
referred to as microorganisms. A lot of eukaryotes are multicellular, thus, are larger
in size because of the greater number of cells their bodies contain.
Recently, prokaryotes have been divided into two domains, namely: Archaea
and Bacteria. The eukaryote group was retained and now consists the third domain
(Eukarya) that includes protists, fungi, plants and animals. Table 1 shows an example
of how organisms are classified.

227
Table 1. Sample classification of organisms
Category
Domesticated
Cat
Dog Bangus Wolf Lion
Kingdom Animalia Animalia Animalia Animalia Animalia
Phylum Chordata Chordata Chordata Chordata Chordata
Class Mammalia Mammalia Actinopterygii Mammalia Mammalia
Order Carnivora Carnivora Gonorynchiformis Carnivora Carnivora
Family Felidae Canidae Chanidae Canidae Felidae
Genus Felis Canis Chanos Canis Panthera
Species catus familiaris chanos lupus leo
Q4. Which organisms in Table 1 are similar up to the Order category?
Q5. Which organisms are most closely related? Why do you say so?
Q6. Can a dog and a wolf produce fertile offspring? Explain your answer.
Recall in Activity 1 that local and common names created confusion. So,
organisms also need be to given names for easier filing of information and reference
by people. How are organisms named?
Q7. Examine the row for species in Table 1. What have you noticed?
For any organism identified, a Scientific Name is given. In this way, every
scientist and other people from different places would use the same name for the
same organism. This is what you see in the species row for each of the organisms.
You must have observed that a scientific name consist of two names.
Q8. What does the first one refer to in the table? What about the second name?
This way of naming organisms is referred to as the binomial system of
classification. Also take note that scientific names are in the Latin language and are
italicized.

228
You should know, however, that researchers may differ in classifying
organisms. It is important to bear in my mind that with further researches and
discoveries this system of classification may change as more information are
gathered about organisms found all over the Earth.
Early studies of organisms resulted to only the two-kingdom classification
system. Later, with the invention of the microscope and with more evidences gathered
about different forms of life, various scientists proposed three, to four, then, five and
later to six or even eight-kingdom classification. Here, the six-kingdom classification
will be used namely: Archaebacteria, Eubacteria, Protist, Fungi, Plant, and Animal
kingdoms.
Archaea Domain: Kingdom Archaebacteria
Organisms that belong to this kingdom are all microscopic. They live in
various places, some even in the most severe environments. Methanogens,
halophiles and thermophiles are examples of archaebacteria.
Do you know that methanogens can survive in places where there is no
oxygen? Some members of this group inhabit digestive tracts of animals and ponds
where animal, human and domestic wastes are treated (Figure 1). Methanogens are
also present on bottoms of lakes, swamps and rice fields. An important characteristic
of this group is they produce methane gas. If you live near rice paddies and swamps
the bubbles that pop at the water surface is methane.
(a) (b)
(Source: Philippines. Department of Education. (2009). Science and Technology II. Textbook (Rev. ed.). Pasig
City: Instructional Materials Development Corporation. p.243.)
Figure 1. Examples of methanogens. (a) Methanobacterium ruminatum, from
cow stomach undergoing division, and (b) Methanospirillum hungatei, from
waste treatment ponds (bar scale = 1 m). The symbol m means
micrometer. 1 m is equal to 0.001 m.

229
Methane is utilized as biogas, a cheap alternative source of energy. There
are already communities and industries which obtain energy for their lighting and
cooking fuel needs from the biogas technology.
If you live in areas which make salt, have you observed the orange or yellow
color in salt ponds? This is due to the presence of halophiles. These archaebacteria
are adapted to very salty environments. Examples are Haloccocus dombrowski and
Halobacterium salinarum.
Q9. Read about the Dead Sea and the Great Salt Lake of Utah, USA. What do
these have in common?
Figure 2 below are examples of thermophiles. This group of archaebacteria
can live in places with high temperature. These areas include volcanic hot springs
with temperatures from 80 to 110C. They also inhabit the small deep sea openings
where hot water with temperatures higher than 250C come out. Thermophiles turn
hydrogen sulfide (H2S) released from these openings to food for other organisms
and in turn are provided essential nutrients by the former.
(a) (b)
(Source: Philippines. Department of Education. (2009). Science and Technology II.
Textbook (Rev. ed.). Pasig City: Instructional Materials Development Corporation. p.242).
Figure 2. Electron micrographs of thermophiles (a) Pyrodictium
occcultum and b) Pyrococcus furiosus (bar scale = 10 m).
10 m = 0.01 mm.
Some members of archaebacteria also survive acidic and even cold
environments.

230
Bacteria Domain: Kingdom Eubacteria
Members of eubacteria are unicellular and microscopic. They are referred to
as the true bacteria and are usually called the “bacteria” group. Their cell walls are
made of peptidoglycan, a carbohydrate.
Q10. What comes into your mind when you hear the word bacteria?
Bacteria consist of a very diverse group. They have varied shapes (Figure 3).
They can be found in almost all kinds of places, in soil, water and air. Some are
present in raw or spoiled food; others live in or on other organisms including your
body. You must have known that they also cause disease and harm to other
organisms. But most importantly, bacteria have a variety of uses for the environment
and for humans.
(Adapted from: Philippines. Department of Education. (2009). Science and Technology II. Textbook (Rev. ed.). Pasig
City: Instructional Materials Development Corporation. p.246).
Figure 3. Basic shapes of bacteria.
Q11. Study Figure 3. Describe cocci, bacilli, and spirilla.
Bacteria are classified according to shape as shown in Figure 3. Also notice
that cocci (sing. coccus), are differently arranged. They can form pairs (diplococcus),
chains (streptococcus), or clusters (staphylococcus). Bacilli can also occur in chains
(streptobacillus).
Most of the time, you probably think of diseases when bacteria which you
refer to as “germs” in the early grades is mentioned.
Are you aware that when your oil glands swell and result to pimples, they are
infected with the bacterium Propionibacterium acnes? A lot of human diseases are
caused by bacteria. Tuberculosis, one common disease in the Philippines, is caused
by bacterium Mycobacterium tuberculosis.

231
Have you heard about the rise of leptospirosis cases in the recently flooded
areas in a number of places in the country? Leptospirosis is a bacterial infection due
to exposure to the spirochete bacterium, Leptospira interrogans. These bacteria are
present in the urine and tissues of cattle, pigs, horses, dogs, rats, and wild animals. It
has been found out that the largest number of leptospira bacteria are in the urine of
rats. Anybody can be infected through contact with water, soil, food and vegetables
that are contaminated with urine of these animals. The bacteria enter the body
through cuts in the skin or surfaces of the eyes or nose. It is important for you to
know that the disease is preventable and treatable with antibiotics.
Q12. Can you think of ways by which you can avoid leptospirosis?
Bacteria also cause diseases in animals. Bacillus anthracis is responsible for
the disease called anthrax. The bacterium is found in the soil and can survive for
many years. The disease affects animals like cows and carabaos but can be
transmitted to humans. Skin anthrax occurs in the Philippines through contact with
animal tissues or their products. Inhalation and intestinal anthrax caused by inhaling
spores and eating of contaminated or undercooked meat, respectively, are more
deadly. It is strongly advised to refrain from eating meat of dead animals suspected
to have died of anthrax. In the early 2000’s there was a worldwide threat of using
anthrax spores to kill people in what is termed as “biological” warfare.
Q13. Who do you think are the people who are likely to be infected with anthrax?
Antiobiotics are substances that kill or inhibit disease-causing organisms. Do
you know that certain bacteria are used to produce antibiotics? Streptomycin, an
antibiotic used to treat tuberculosis and certain types of pneumonia is made by
Streptomyces griseus. Streptomyces venezuelae on the other hand produces
chloramphenicol used in killing bacteria that cause typhoid fever and skin infections.
Escherichia coli is naturally found in the large intestine of humans. It feeds on
partially digested food moving from the stomach to the small intestines. These
bacteria meanwhile provide the much needed vitamin B12 that otherwise the human
body cannot produce. E. coli however, once present in other areas in the body can
produce poisons causing diarrhea or kidney damage and even death.
Do you know that many of these bacteria are also involved in making some of
the foods or drink you like?

232
Some bacteria convert cheap materials into useful products such as food.
Examples are Lactobacilli bulgaricus and Streptococcus thermophilus of the lactic
acid bacteria group. These are specifically involved in making sour milk or yogurt.
Yogurt is made by adding a culture of Lactobacillus bulgaricus present in the starter
to skimmed milk powder. Lactase in the bacteria changes the milk sugar into lactic
acid. When this occurs, proteins in milk curdle which gives yogurt its semi-liquid
texture. Be familiar with these bacteria by doing the following activity.
Activity 2
How do bacteria in yogurt look like?
Objectives:
1. identify bacteria present in fermented food or drink
2. describe bacteria observed under the microscope
3. explain the use of bacteria in food or drink making
Materials Needed:
2 droppers diluted yogurt
coverslip glass slide
microscope methylene blue
Procedure:
1. Place a drop of diluted yogurt on a slide.
2. Add a drop of methylene blue and cover with a cover slip.
Q14. What is the purpose of adding methylene blue to the specimen?
3. Observe under the LPO and HPO of the microscope.
TAKE
CARE!
Follow
precautionary
measures in
handling the
microscope.

233
Q15. Describe what you see under the HPO.
Q16. Which are Lactobacillus bacteria in yogurt? Which are Streptoccus bacteria?
Q17. What are your reasons for saying so?
Have you heard about “oil-eating” bacteria? Some members of eubacteria are
able to break down or remove pollutants through the process of bioremediation.
Scientists at University of the Philippines-Diliman’s Molecular Microbiology
Laboratory have identified a number of bacteria which can help solve the problem of
oil spills in oceans and seas through this technology. These are Pseudomonas
aeruginosa, Acinetobacter baumanii, Paenibacillus thiaminolyticus, Bordetella
bronchiseptica and Lysinibacillus sphaericus.
Another group of bacteria (Figure 4), the cyanobacteria are plantlike
because they have chlorophyll-containing cells. Most of them are single-celled, some
form filaments, while others form spores. Cyanobacteria grow in ditches, esteros, or
in moist places like gardens and sidewalls where light is present. In Northern Luzon
people eat raw Tab-tab (Nostoc) as salad. Spirulina cells are rich in protein, thus,
have been grown to produce Single Cell Protein (SCP). It is used as swine and cattle
feed and is also recommended as food for humans.
Textbook (Rev. ed.). Pasig City: Instructional Materials Development
Corporation. p.249.
Figure 4. Examples of cyanobacteria are (a) Lyngbya,
(b) Microcoleus, (c) Oscillatoria, (d) Nostoc, and
(e) Spirulina.

234
Anabaena azollae, another cyanobacterium is important in agriculture. It
converts nitrogen in air into compounds usable by plants for growth and
development. The same is being done by the Rhizobium group of bacteria. They are
present in the root nodules of legumes.
Q18. What is the advantage of planting legumes together with other crops?
Certain bacteria, like Bacillus thuringiensis, have been developed into a
microbial pesticide. It is used to control pests and and insects carrying disease-
causing organisms.
Protists
Earlier you were introduced to protists. Are they prokaryotes or eukaryotes?
What can you remember from Grade 7 about algae? How were they classified?
Members of Kingdom Protista come from unrelated ancestors. This grouping
is referred to by biologists as an artificial grouping. The inclusion of the large number
of unicellular organisms under this kingdom is just for convenience.
Protists differ in size, movement and method of obtaining energy. Though
most of protists are microscopic, some can grow to as high as several meters.
In terms of method in obtaining energy, protists are classified into three
groups. Phototrophs produce their own food. Heterotrophs feed on other
organisms. This group is also divided into a group with no permanent part for
movement, those with cilia, and those with limited movement. Others which are
nonmotile and form spores belong to the sporozoan group. Members of this group
are all parasitic.
Phototrophs are like plants in that they have chlorophyll. This group includes
the algae, dinoflagellates, and euglenoids.
Algae may be green, golden, brown or red. The chlorophyll in green algae is
not masked in contrast to the other members of the group. The carbohydrate that
green algae produce is stored as starch. They grow on wet, humid rocks or bark of
trees, in non-flowing canals, in seas, freshwater bodies and even polluted
waterways. Green algae differ in size and shape. Some are unicellular; others form
colonies, sheets, filaments, tubes and ribbons (Figure 5). Some green algae are
edible. The marine green alga Caulerpa lentillifera is eaten fresh as salad.

235
(a) (b) (c) (d)
(Source: Philippines. Department of Education. (2009). Science and Technology II. Textbook (Rev. ed.).
Pasig City: Instructional Materials Development Corporation. p.255).
Golden algae (Figure 6) cells also contain chlorophyll but is masked by
yellow pigments. Members of this group are mostly microscopic. They store food in
the form of leucosin oil or chrysolaminarin.
(
S
o
u
r
c
e
:
Philippines. Department of Education. (2009). Science and Technology II. Textbook (Rev. ed.). Pasig City:
Instructional Materials Development Corporation. p.256).
Figure 6. Diversity in shape of diatoms, a golden algae.
In one of your trips to the seashore, did you notice something like one of
those shown in Figure 7? If your answer is yes, you have seen brown algae! Most
members of this group are marine so you can see them just lying around on the
beach. Brown pigments mask their chlorophyll.
Figure 5. Examples of green algae (a) Chlorella, (b) Draparnaldia,
(c) colonial Pediastrum, and (d) filamentous Spirogyra

236
Figure 7. Some common brown algae found in the marine waters
of the Philippines
Brown algae are the largest of the algae species. Giant kelps, a member of
this group can grow to more than 30 meters in length. This group of algae store
carbohydrate in the form of laminarin.
Do you know that brown algae have something to do with your favorite ice
cream or toothpaste? Some members of the group contain alginic acid used as an
ingredient in making these two, including candy and cream cosmetics.
Leaflike and bubblelike structures called bladders are present in brown algae.
They float near the water surface where light is present.
Q19. What is the importance of bladders in brown algae?
Have you heard eaten gozo? Eucheuma muricatum (Figure 8) or kanot-kanot,
another name for gozo, is a member of the red algae group. The group differs from
the rest of the algae by storing food in the form of floridean starch. As their name
suggests, red pigments mask their chlorophyll.
Laminaria

237
(Source: Philippines. Department of Education. (2009). Science and Technology II. Textbook
(Rev. ed.). Pasig City: Instructional Materials Development Corporation. p.257).
Figure 8. Examples of red algae.
Red algae can change color depending on whether they are exposed or
hidden from light. When they are exposed to light, they are bright green in color. If
they grow without much light, they are colored red. Members of the group consist of
both microscopic and large multicellular organisms. Most of them are found in marine
waters.
There are species in the group that help form coral reefs because of their
ability to produce calcium carbonate. Economically, E. muricatum is useful being a
source of agar and carageenan. If you are fond of eating gulaman, note that it comes
from agar. Eucheuma farming has become a source of livelihood in certain areas in
Central Visayas and Mindanao. Likewise, Gracilaria salicornia (Figure 8) is an agar
source and edible too.
Q20. Why is light important to algae?
Most members of dinoflagellates live in oceans and seas. They are mostly
unicellular. Some occur as single organisms, while others form colonies. An important
dinoflagellate to know is Pyrodinium bahamense var. compressum (Figure 9). They
are the ones that cause “red tide” when present in large numbers. During red tide,
people should not eat clams and mussels in the affected areas. This is because these
organisms might have fed on the dinoflagellates which produce toxins and cause
paralysis of the diaphragm that can lead to death.
Eucheuma muricatum Gracilaria salicornia

238
(Adapted from: Philippines. Department of Education. (2009). Science and Technology II.
Q21. What is the danger of eating clams when red tide occurs?
The euglenoids are microscopic and unicellular. Euglena belongs to this
group. It lives in freshwater bodies. Organisms of this group have a whiplike flagellum
for movement. Some euglenoids have chlorophyll.
Euglena has an interesting characteristic of getting food. When light is
available to, it makes food utilizing chlorophyll. In the absence of light, it absorbs
nutrients from dead organic matter.
Heterotrophs with no permanent structure for movement include the
radiolarians, foraminiferans and amoeba (Figure 10). They move by means of the
pseudopods or pseudopodia. Notice the extensions at the sides of these organisms.
These temporary extensions are formed when changes in the cytoplasmic
concentration occur within the cell. This change causes the cell membrane to contract
and enable the organism to make a creeping movement. Pseudopods may form as
they are needed.
Q22. Compare pseudopods of foraminiferans, radiolarians and amoeba.
(Source: Philippines. Department of Education. (2009). Science and Technology II. Textbook (Rev. ed.). Pasig City:
Figure10. Examples of heterotrophs using pseudopodia for movement.
Figure 9. Pyrodinium bahamense var. compressum, the
red-tide causing dinoflagellate.
foraminiferans radiolaria
n
amoeba
pseudopodia

239
Entamoeba histolytica is a harmful species of amoeba living in freshwater
bodies. If present in underground water, it can contaminate drinking water. Once this
happens, the gastrointestinal tract is infected causing amoebiasis. If the protist
invades the intestinal lining it leads to amoebic dysentery. Proper sanitation must be
practiced to ensure clean and safe drinking water.
Another heterotroph, the paramecium, moves using the cilia attached to
parts or all over its body. The ciliate group are free-living and present in both fresh
and salt water. They also use the cilia to get food. Other examples are the Didinium
and Vorticella.
Slime and water molds are motile in a certain stage in their life cycles. Thus,
they are considered to be heterotrophs with limited movements. Slime molds are
usually the colored yellow, orange, or whitish growths that you may see on damp
rotting logs. They feed on bacteria and decaying plant material in the same manner
as an amoeba does. Water molds are white cottony growths on dead fish or plant
parts that you might see floating in water. Certain species of water molds are parasitic
on corn, grapes cabbage and many other important crops.
Members of the sporozoan group as mentioned earlier cannot move on their
own. They may be free-living and parasitic. Some like four species of Plasmodium are
harmful for they cause malaria, a serious disease in humans. This malaria-causing
sporozoan is transmitted to humans by Anopheles mosquito. In the Philippines
malaria is still constantly present in certain areas.
Another group of heterotrophs include the flagellates. They are unicellular and
they use one or many of their threadlike flagella to move. Some of them exist as
single organisms though others form colonies. There are parasitic and free-living
flagellates. Two important species to study are Giardia lamblia and Trypanosoma
gambiense (Figure 11a) because they affect humans. G. lamblia cause severe
diarrhea, while T. Gambiense is responsible for Gambian sleeping sickness.
Trichonympha (Figure 11b) is beneficial to other organisms. It lives in the
intestine of termites. Since termites cannot digest the wood that they eat,
Trichonympha do it for them. Termites in turn give them a home and food to eat.
Figure 11. (a) Harmful and (b) beneficial flagellates
Trypanosoma
(a)
Trichonympha
(b)

240
Q23. Give at least five uses of protists.
Fungi
You must have seen the orange colored growth on spoiled corn, the gray to
black or white spots on a three-day old bread left in a warm and humid or moist place.
Or the kabuti, that your father gathered from the woods and yeast used in making
bread. All these are fungi.
You first encountered the eukaryotic fungi in Grade 7. You have also learned
that they have no chlorophyll thus, cannot produce their own food. Some are
parasites, because they survive by living on a host organism. Others feed on
decaying matter and are called saprophytes. Fungi also have cell walls but are made
up of chitin.
Fungi undergo asexual reproduction by forming buds and many spores.
Actually, the black thing you see in fungi are spores in large numbers. These spores
are abundant in the environment as they are carried easily by wind, water, animals, or
humans. When spores land in areas suitable for their growth, new fungus develops.
Fungal bodies consist of hyphae with rootlike rhizoids that attach them to the
substrate on which they grow. Hyphae absorb and provide nutrients to the fungi by
extending downward into the substrate. Fungi also reproduce sexually when male and
female hyphae join together.
Fruiting structures extend upward where spores are produced. Fungi are
classified according to the kind of fruiting structures they form (Figure12). In bread
mold Rhizopus, spores are produced in the sporangium.
Figure 12. Differences in the fruiting structures of three groups of fungi.
(a) occurs in bread mold, (b) in yeasts and (c) in mushrooms.

241
Q24. Where are spores of yeasts produced? How are yeast spores called?
Q25. Where are mushroom spores produced?
Q26. What is the advantage of the large numbers of spores produced by fungi?
Examples of fungi used as food are Volvariella sp. and Pleurotus sajor-caju
(oyster mushroom). Others utilized in soy sauce making include the yeast,
Saccharomyces rouxii and the mold, Aspergillus oryzae. Yeast is an ingredient in
making bread.
Fungi are involved in decomposing organic materials. Decomposition is made
faster using Trichoderma harzianum. An important mold to mention is Penicillium
notatum. It is used in making penicillin, a drug that kills disease-causing bacteria.
Some fungal species however, can be harmful to other organisms and
humans. The mold Aspergillus flavus produces aflatoxin, a poisonous substance. If
large amounts of aflatoxin in moldy corn, garlic or peanuts are ingested, both poultry
and humans can be poisoned. The parasitic fungi Trichophyton mentagrophytes
and T. rubrum, cause athlete’s foot. T. rubrum can also cause ringworm.
Q27. From what you know and have observed about fungi, in what conditions do they
grow?
The Plant Kingdom
Recall what you know about plant cells. Do they have chloroplasts? What are
their cell walls made of?
You knew earlier that plants belong to the eukaryote group. They are
multicellular and because they have chlorophyll, they can make their own food.
Plants consist of two big groups: those which do not have tissues to transport water
and food (nonvascular) and those that have this transport system (vascular).
Nonvascular Plants
Have you noticed green patches attached to stones or cement walls especially
during the rainy season or in moist, wet and shady areas?
Liverworts, mosses and hornworts (Figure 13) are nonvascular plants. They are
attached to the places where they live by means of their root-like rhizoids. These
rhizoids absorb water and nutrients instead of true roots. They also do not have true

242
stems and leaves so they grow very close to damp grounds, stone walls or tree
trunks.
Photos courtesy of Addie A. Saliva
(a) (b) (c)
Figure 13. Example of nonvascular plants (a) liverworts, (b) mosses,
and (c) hornworts.
Q28. How do liverworts, mosses and hornworts differ in appearance?
When nonvascular plants mature, they also form different reproductive
structures. Liverworts develop “umbrella-like” structures that produce eggs and
sperms. Notice in Figure 13b the capsules at the tip of thin stalks in mosses. These
capsules contain the spores. In hornworts, you see them as thin “thorn-like”
structures.
Nonvascular plants may seem very small but they play an important role in
the environment. They provide oxygen to many organisms. Their “carpetlike” growth
covering large areas in hilly grounds prevent erosion and increase the capacity of
soil to hold water. Dried Sphagnum or peat moss is used to wrap plants and
breakable items during transport. Gardeners use them to retain more water in the
soil for important crops. Old, dead sphagnum form thick deposits called peat, which
is used as fuel in some places.
Q29. Why do you think nonvascular plants cannot grow very large or tall?
Vascular Plants
From studying water-dwelling organisms, you will now deal with ferns which
thrive on land with true roots, stems and leaves. Ferns also reproduce by spores.
More than 900 species of ferns can be found in moist, shaded and mountainous
areas in the country. They exhibit diversity in size from a few millimeters to about 12

243
meters. Some ferns still inhabit freshwaters (Figure 14b), while others grow on tree
trunks. The Anabaena cyanobacterium you studied earlier are present in the
underside of azolla, a water fern.
Q30. Examine Figure 14a. Can you explain how it earned its name?
Have you heard of tree ferns (Figure 14c)? At first glance, you may think it is
a tree with a sturdy trunk. You should know that they are not strong as woody plants.
Photo by: Alvin J. Encarnacion Photo courtesy of Michael Anthony B. Mantala
Giant fern, Angiopteris sp. Salvinia sp.
(a) (b)
Photo by: Karina Luth Discaya
Cyathea sp. (tree fern)
(c)
Figure 14. Examples of Philippine
ferns (a) Giant fern, (b) water fern
and (c) tree fern.

244
Q31. How will Azolla help rice if they are grown together in fields?
With the fern’s ability to make food, they too provide other organisms with
food and oxygen. You are also familiar with the use of ferns as plant decoration.
Some Philippine handicrafts are made from fern fibers like nito.
Q32. Give other uses of ferns in your locality.
Gymnosperms
Seed plants consist of those which bear seeds contained in cones and those
inside a protective layer of tissue. Plants whose seeds are borne in cones (Figure
15a) are called gymnosperms. Examples of gymnosperms are the conifers, cycads,
ginkgoes, and gnetophytes. Many conifers like pine trees grow in cold countries and
in elevated places in warmer climates. They are woody trees and have tough needle-
like leaves.
(Source: Philippines. Department of Education. (2009).
Science and Technology II. Textbook (Rev. ed.). Pasig City:
(a) (b)
Figure 15. (a) Benguet pine cones and (b) a Ginkgo biloba tree growing in Tokyo,
Japan.
Q33. Where in the Philippines would pine trees likely grow?
Cycads are short, palm-like plant growing in tropical and subtropical areas. In
the Philippines they are seen in well-landscaped hotels and parks. Gnetopytes are
represented by Welwitschia which can be found in Namibia, Southwestern Africa.
Photo by Rodolfo S. Treyes

245
Gymnosperms are sources of quality wood for making plywood and furniture.
They also supply pulp to paper-producing factories. Other species provide resin,
used in making perfumes and varnishes. Pine cones are popular Christmas
decoration items.
Q34. How would uncontrolled cutting of pine trees, for example, affect the forest
ecosystem?
Angiosperms
You are most familiar with members of this group as you may have played
with their flowers even at an early age. In the earlier grades, you have learned how
varied they are in terms of parts and habitat. You also studied about what parts are
involved in reproduction and ways by which they reproduce. They are also called
flowering plants since flowers, as well as fruits, are involved in their reproduction and
development.
Angiosperms can be classified according to their lifespan. Annuals live for a
year or one growing season and die like rice and corn. Biennials develop roots,
stems and leaves during the first year, produce seeds on the second year, then die.
Perennials live for many years, usually producing woody stems like tsitsirika,
bamboo, and trees.
Leaves of angiosperms also differ in their arrangement in the stem. Study
Figure 16.
Coffea arabica (coffee) Allium sativum (garlic) Anacardium occidentale (cashew)
Figure 16. Differences in arrangement of leaves in plant stems
Q35. Which plant leaves are arranged alternately, radially and opposite each other?

246
Flowering plants are also classified as to the number of cotyledons present in
their seeds. Monocotyledons or monocots have only one cotyledon present, while
dicotyledons or dicots have two. Coconut and grasses are examples of monocots.
Gumamela and mango are dicots. Other differences among the two are exhibited in
characteristics of some of their parts as shown in Figure 17.
(Rev. ed.). Pasig City: Instructional Materials Development Corporation. p.276).
Figure 17. Characteristics of monocots and dicots

247
Q36. In terms of leaf venation, is santan a dicot or a monocot?
Q37. How about bamboo?
Recall the structure of the flower you studied in Grade 7. Angiosperms can
also be differentiated by means of their flower parts. A flower may have both petals
and sepals or may have sepals or petals only. Others have stamens, petals and
sepals attached to the ovary. Some have their petals separated, others are united.
You can observe several flowers from different plants and you may see other
differences or similarities among them.
Importance of Angiosperms
Look around you. Think of what you have eaten or what you have used
earlier. Were there any from this group of plants mentioned that you have eaten, or
in any way used?
Angiosperms of importance worth mentioning are Filipinos’ staple food: rice
for most of us, corn in some areas; vegetables like camote tops, malunggay,
cabbage, carrots, saluyot and squash.
Q38. Make a list of the uses of coconut that you know.
Many of our agricultural products, both fresh and processed are exported.
Examples are banana from Davao, mango from Guimaras, coffee from various
provinces, pineapple from Bukidnon and tobacco from provinces in Northern Luzon.
Furniture made from rattan are also sold to various countries abroad. Sugar cane
from different provinces is also another grown for export.
Many angiosperms have been developed to prevent and cure some
diseases. Lagundi, sambong, ampalaya, and banaba to name a few are now
commercially available for specific ailments.
Q39. Describe how birds, butterflies and spiders benefit from members of the
angiosperms.
Q40. What is the greatest contribution of plants to living things on Earth?
Harmful Plants
Some plants can be harmful to animals, humans, and even to other plants.
Care must be taken that cows and other livestock should not graze in areas where
sorghum grow. It is known to cause cyanide poisoning in livestock as young leaves
contain a poisonous substance.

248
Jatropha curcas (tuba-tuba/tubang bakod) is popular due to its being an
alternative source of bio-fuel. Although known to have medicinal properties, its seed
is poisonous. The fruits which are usually eaten by children cause stomach pain,
burning sensation in the throat and vomiting. Manihot esculenta (cassava) if boiled
with its bark on it can be poisonous. The bark contains hydrocyanic acid. It is advised
that during cooking, the pot cover should be removed for the cyanogas to escape. A
word of caution: do not eat any part of a plant which you are not familiar with.
Echinochloa crus-galli (dawa-dawa) and Digitaria sanguinalis (saka-saka) are
weeds which are alternative hosts to abaca and corn mosaic viruses.
Q41. What harm can weeds do to crops if they grow together?
The Animal Kingdom
What can you remember about the characteristics of animal cells? How do
animals differ in size, shape or habitat? How do they respond to their environment?
Animals differ in size and shape. In Grade 7, you learned that small ones
have few cells while big ones can have up to trillions! Some animals can live inside
other animals. Others are found in fresh or marine waters and some in every habitat
on land. They reproduce either sexually or asexually.
Despite their differences, animals share basic characteristics. By now you
must have known that this group are eukaryotic and multicellular. Some get
nourishment from other animals, others eat plants while others feed on protists. You
knew that animal cells have no cell walls. But they have cells involved in movement
though some species are nonmotile. Animals also have cells that transmit messages
throughout their body.
Q42. In your observation, how are animals distinguished from the other groups as to
their reaction to stimuli?
Animals consist of two major groups, the invertebrates and vertebrates.
Invertebrates lack backbone which is present in vertebrates. In this section, you will
discover the diverse characteristics, uses and roles in the environment of nine in
about thirty five animal phyla.

249
Sponges
Sponges, the simplest animals, belong to Phylum Porifera. They live in
shallow and deep oceans. The young of sponges are motile, while adults are
attached to solid materials like rocks. The body of a hard sponge is supported by a
“skeleton” called spicules, made of either glasslike silica or calcium carbonate. A
network of protein fibers supports soft sponges. This is the one used for bathing and
washing.
Figure 18. Structure of a sponge showing how water and food and waste
materials move in and out of its body, respectively.
Water and food enter through the pores into the sponge body (Figure 18).
Food is brought to the collar cells with the beating of flagella. Waste water and
materials go out of the sponge through the osculum.
Cnidarians
Members of Phylum Cnidaria consist of animals whose tentacles contain
stinging cells called nematocysts. These poison-filled structures are used for
defense and to capture their prey or food. Once released, this can be painful and
even fatal like an attack by jellyfishes.
Corals form colonies of various colors and secrete a hard skeleton. These
accumulate to form coral reefs which are of great importance as they are one of the

250
world’s most productive ecosystems. A coral reef is where fishes and other marine
organisms breed. At present however, coral reefs are destroyed by pollution from oil
spills and dynamite fishing. Add to these the silt and sediments that flow down from
the mountains because of farming, mining and logging activities.
Hydra represent freshwater cnidarians. Other marine cnidarians are shown in
Figure 19.
(Source: Philippines. Department of Education. (2009). Science and Technology II. Textbook (Rev. ed.). Pasig City: Instructional
Materials Development Corporation. p.287).
Figure19. Variety in marine cnidarians.
Q43. Which cnidarians are attached? Which are free-swimming?
Flatworms
The flatworm group belongs to Phylum Platyheminthes (in Greek platys
means flat, helmins means worm). As their name suggests, they are flat and ribbon-
like organisms. Flatworms are found in freshwater, in wet places and marine waters.
They include the free-living or nonparasitic worms, the parasitic flukes, and the
tapeworm group. Planaria is an example of a free-living flatworm. It lives in moist
surfaces, under rocks in ponds, rivers and even aquariums. Flukes are parasites that
live in other animals including humans.

251
Tapeworms are also parasitic flatworms like flukes without a digestive system. It can
have fish, cows and pigs as hosts. Humans can be infected with tapeworms if they
eat uncooked fish, beef or pork.
Q44. Why do you think parasitic flatworms do not have a digestive system?
Roundworms
Roundworms are members of Phylum Nematoda. Compared to flatworms,
roundworms also known as nematodes have long, cylindrical and slender bodies.
Some roundworms are free-living while others are parasites of animals and plants.
The free-living ones are important as they are decomposers in the soil in both marine
and freshwaters. A lot of them are found in decaying organic matter. Parasitic
roundworms can be found in moist tissues of plants and animals. Heartworms for
example can infect dogs and cats. Humans can be infected with parasitic
roundworms such as trichina worms, hookworms and the more common pinworms
and Ascaris (Figure 20) afflicting children.
Figure 20. A male and female Ascaris with its internal parts shown.
Digested food is taken in the mouth and exit in the anus.

252
Q45. Study Figure 20. How many openings does an Ascaris body have?
Segmented Worms
The third group of worms among the animal phyla belongs to Phylum
Annelida. Also known as annelids, these animals are characterized by a segmented
or repeated body parts. This makes them move easily and with flexibility. Annelids
are mostly found crawling in moist soil or swimming in sea and freshwaters.
Examples of annelids are earthworms, polychaetes and leeches. Most polychaetes
are marine living in tubes attached to rocks or sand. They get floating food through
the feathery gills. Sandworms are examples of polychaetes.
Annelids have nervous, circulatory, digestive and excretory systems. Each
segment contains most of the internal structures of these systems. Gas exchange
only occurs by diffusion through their skin. This is why earthworms need to be in
moist places like under rocks or stay buried in the soil. As they feed and burrow
through the soil, they get nutrients and eliminate wastes (castings) through the anus.
In this way they aerate the soil and the castings serve as fertilizer.
Leeches are blood-sucking annelids. They have suckers in both ends of their
bodies that are also used to attach themselves to their hosts. They secrete an anti-
clotting chemical that has been used in medicine.
Mollusks
Mollusks (Phylum Mollusca) are soft-bodied invertebrates with most of them
covered by a shell. They have complex respiratory, reproductive, circulatory,
digestive and excretory systems functioning together for their survival. The mollusk’s
body has three parts: a muscular foot for locomotion, a mantle that produces the
shell, and the visceral mass that contains their internal organs. Mollusks consist of
three classes: the Gastropods, Bivalves and Cephalopods.
Q46. Study Figure 21. How would you describe univalves? bivalves?

253
(Rev. ed.). Pasig City:Instructional Materials Development Corporation. p. 291.)
Figure 21. Examples of mollusks
Gastropods, also called univalves, as you have observed, has only one shell.
They are mostly marine with freshwater and terrestrial members. Those living in seas
have gills for breathing and those on land use the lining of their mantle as lungs. Sea
and land slugs, as well as nudibranchs are examples of gastropods.
You may be most familiar with the bivalves as you see them on your dining
table more often. These molluscs as you have observed consist of two shells
attached to each other. Some bivalves are attached to rocks while others remain in
the sand or mud. They use their mantle cavity to feed by trapping suspended
particles in water and for gas exchange. Mussels, oysters, and clams are bivalves.
The cephalopod group include the squid and cuttlefish with internal skeleton.
The chambered nautilus has external skeleton while the octopus is shell-less. All
cephalopods are described as the most active mollusks, moving very fast using arms
and tentacles in catching prey.
Q47. Into which group would you classify halaan? the giant African snail?Tridacna
(taklobo)?
Many mollusk species are utilized as food like tahong (mussels), talaba
(oyster), halaan (clam), scallops, and kuhol or suso to name some. Other species
are made into decorative items.
Golden kuhol, however, has become a pest to rice and other crops. They eat
a lot of plant leaves and reproduce rapidly. The giant African snail Achatina fulica
was found to be an intermediate host to a rat lungworm that causes meningitis.

254
Echinoderms
You can be fascinated by the star-shaped sea star or the spine–studded sea
urchin and the appearance of the sand dollar. Along with the brittle star and the sea
cucumber, they belong to Phylum Echinodermata. All echinoderms are found in a
marine environment. Sea lily, another echinoderm, is rooted in the sand at the
bottom of the sea, while sea cucumber burrows in mud of deep or shallow waters.
Parts of most echinoderms radiate from the center of the body. They also
have spines which are extensions made of hard calcium. Under the skin, these form
an internal skeleton called the endoskeleton.
Sea stars have the ability to regenerate. A cut arm can easily regrow into a
new sea star.
Unique to echinoderms is the presence of the water-filled tubes that spread
out to form the tube feet (Figure 22). Tube feet are used for getting food, moving
around and gas exchange.
Textbook (Rev. ed.). Pasig City: Instructional Materials Development Corporation. p. 294.)
Figure 22. Sea star showing (a) arms radiating from the center of the
body, (b) spines, and (c) tube feet.

255
Echinoderm species which are edible include the sea urchin and sea
cucumber. Holothuria edulis, a sea cucumber, is dried and used as ingredient for
chopsuey and soups.
Remember the role of coral reefs in the environment? Sea urchins are
important to coral reefs because they consume algae that otherwise overgrow and
can kill the corals. In contrast, the sea star, crown of thorns, are predators of coral
polyps posing a threat to the existence of the reefs.
Arthropods
Have you observed what grasshoppers, spiders, crabs and centipedes
have in common? If you take a look at each of these you will notice that they have
jointed legs. These animals belong to Phylum Arthropoda. The group is considered
the most successful of all animal phyla as they are present in almost all types of
habitats. There are arthropods that walk or crawl, some can fly, while others swim
in salty and freshwaters.
Recall in Grade 6, you learned that arthropods have an exoskeleton. This
is made of chitin and varies from thin and flexible to thick and hard exoskeletons.
These animals grow a new skeleton many times in their life to give way to growth,
specifically, increase in size through the process of molting.
Q48. How do arthropods differ from echinoderms?
Q49. What could be the function of the exoskeleton in arthropods?
Arthropods are grouped based on the type of exoskeleton, the number of
body sections and the kind of appendages like mouth parts present. Appendages
may be used for avoiding predators, getting food, walking or swimming.
Crustaceans form one group of arthropods which includes water fleas, crabs,
shrimps, lobsters and barnacles. They have hard exoskeletons and have mandible
to bite and grind food. All crustaceans live in water with the exception of the pill bug.
You see it in the soil as the small creature that rolls into a tiny ball when disturbed.
Aquatic crustaceans have gills for breathing. Many crustaceans are food to humans.
The small ones are eaten by fishes and even whales.
Arachnids have two body sections, most with four pairs of legs and
mouthparts called chelicerae and pedipalps. They use book lungs to respire.
Spiders with thin and flexible exoskeleton are the largest members of the group.
Mites and ticks are parasitic arachnids. They cause itching to some mammals,

256
including humans. Scorpions have a poisonous sting. The horsehoe crab, a close
relative of arachnids, is considered the oldest living arthropod.
Millepedes and centipedes, close relatives of insects have long, wormlike
segmented bodies. They have a pair of antenna and each segment bear a pair or
two legs. These animals live in the soil, under rocks or rotting logs and leaves.
Millipedes have two pairs of legs per segment and roll up when disturbed. They feed
on decaying matter. Centipedes have a pair of legs in a segment. They have venom-
containing claws and feed on earthworms, even other arthropods and small animals.
Insects form the largest group among arthropods. They have three body
sections, three pairs of legs, a pair of antenna and one to two pairs of wings. Insects
are more adapted for flying and have tracheal tubes for respiration. They are present
in great numbers in all kinds of environments except in marine waters. Exoskeleton
of insects as that of a fly is thin. Insects are also successful animals because they
reproduce rapidly. Dragonflies, grasshoppers, aphids, and butterfies are some
examples of insects.
Q50. Which arthropod group has no antenna?
Q51. How do legs of insects and arachnids differ?
An important insect that you should learn about is the mosquito. A species of
this group, Aedes aegypti pose a danger to people of all ages. It carries and
transmits through its bite the virus that causes dengue. The following activity will
describe how this species reproduce and teach you how to control dengue.
Activity 3
What can you do to prevent dengue?
Objectives:
1. describe and classify Aedes aegypti,
2. discuss the life cycle of A. aegypti,
3. identify breeding places of A. aegypti,
4. explain the role of A. aegypti in spreading dengue, and
5. suggest ways of preventing dengue.

257
Materials Needed:
sheet of paper
illustration of life cycle of Aedes aegypti
Procedure:
1. Study the different stages in the life cycle of Aedes aegypti below.
Life Cycle of Aedes aegypti
Q52. How does the adult of this mosquito look?
Q53. Describe the breeding place of A. aegypti.
Q54. In which places in your home, school or surroundings can this mosquito breed?
Name at least 5.
Stage IV:
The adult mosquito stay in cool areas on land after hatching. It flies as
far as one hundred meters to mate and look for food. The male mosquitoes
feed on flower nectar and are usually found near breeding sites. It is the
female mosquito that bites animals and people to feed itself with blood. It
continues the cycle by laying eggs.
Stage I:
Female mosquitoes lay eggs
in clean and non-flowing water.
Examples are rainwater that has
collected in old unused tires and
those in flower vases. The eggs
are white but later turn into shiny
black. Usually this stage may
last for only minutes to two days
in warm climates but can reach a
week in cooler temperatures.
Eggs can survive even for a year
and are immediately hatched
once submerged in water
Stage II:
Mosquito eggs hatch into larva (plural: larvae). It is the second and the
most easily seen stage of mosquito development. A larva always lives in
water and eats a lot of algae and organic matter. It breathes in air from
above the water surface through a tube called siphon. When disturbed, it
dives down to the bottom, so it is also called a “wriggler.” It returns to the
surface to breathe. This stage usually lasts about five to seven days.
Stage III:
The third stage consists of the
comma-shaped pupa which
continue to stay at the water
surface. The pupa breathes
through two small tubes called
“trumpets.” It dives downwards
quickly when disturbed. It stops
eating and grows shorter. Then,
it encases itself with a hard
covering. Inside the pupal case,
it continues to change and grow.
This stage takes only about two
to three days. If the water dries
up before the next stage, the
organism dies.

258
Have you heard about “kiti-kiti”? These are the larvae or wrigglers.
Q55. What do you think will happen to a larva that is removed from water?
Q56. Based on your study of the life cycle of Aedes aegypti, how important is water
to the mosquito?
2. Review your answers to Q54.
Q57. What can you do to stop the reproduction of the dengue virus-carrying
mosquito? Name at least 5.
Q58. Into what group of arthropods would you classify the mosquito and why?
Chordates
Animals belonging to Phylum Chordata have four characteristics that are
present in any of the stages in their life cycle. These are the notochord, the dorsal
hollow nerve cord, gill slits and a post-anal tail. In many chordates, the notochord
later becomes the backbone. Humans being a member of the chordate group have
the notochord, tail and gill slits only in the embryo stage.
However, there are lower chordates that do not have a backbone. Examples
are the tunicates and lancelets. The adult tunicates have only the gill slits present
but the larva stages have all the four features. Tunicates attach to solid materials like
rocks or coral reefs. They are filter feeders, taking in food particles suspended in
water.
Lancelets have the four chordate characteristics present in the adult stage.
They live in the sandy ocean bottom. They are also suspension feeders. Lancelets
move in a fishlike motion using the muscles on both sides of their body.
Vertebrates
Most vertebrates are sea and land dwellers forming the large group of
chordates. The vertebrates’ notochord is replaced by the backbone or the vertebral
column (vertebra, plu. vertebrae). The nerve cord is enclosed by the projections of
the vertebrae. The protected nerve cord enlarges at the anterior end to develop into
the brain. The tail can be the bone and muscle that animals use for swimming in

259
aquatic species. For some vertebrates, the gill slits remain till the adult stage. In
others, these are modified into structures for gas exchange.
Fishes
Fishes are vertebrates found in salty, fresh, cold or even hot water. Most
have scales for protection, paired fins for movement and gills for gas exchange.
Fishes may lay eggs to reproduce or give birth to live young. They are cold bloodied
because their body temperature changes when environment temperature changes.
Certain fishes do not have true teeth or may be jawless as compared to the others.
Jawless fishes belong to Class Agnatha. Examples are the lampreys and hag
fish. Lampreys, being parasites, have tooth-like structures in their mouth that can
attach to bodies of other fishes and feed on their tissues and blood. The hagfish is
wormlike and use a toothlike tongue to eat dead organisms.
Cartilaginous fishes include the rays, skates and sharks. They have a
skeleton made of the soft, flexible protein material called cartilage. Most cartilaginous
fishes are covered with a tough, sandpaperlike skin due to the presence of toothlike
scales. Skates and rays have winglike fins and move in a gliding motion through the
water. Some of them eat floating planktons while others feed on invertebrates at the
bottom of seas and oceans.
Sharks may feed on small fishes or on floating algae. The whale shark
(Rincodon typus), the largest fish, and locally known as butanding is found in marine
waters of Cebu, Sorsogon and Dumaguete.
The diverse groups of bony fishes belong to Class Osteichthyes. These are
the fishes that have an endoskeleton made of hard, calcium material called bone.
Bony fishes are more familiar to you like bangus (milkfish), tuna, goldfish, and tilapia.
The non-familiar lungfish breathes through the lungs in addition to having gills also
for respiration. Eels are wormlike fishes. Figure 23 shows some of the members of
the bony fishes.

260
(Adapted from: Philippines. Department of Education. (2009). Science and
Technology II. Textbook (Rev. ed.). Pasig City: Instructional Materials
Development Corporation. p. 301.)
Q59. Compare the skeleton of the shark and the tilapia.
As food of humans and other animals, you will learn more about the role of
fishes in food chains and food webs which you will study in the next module.
Amphibians
Amphibia means “double life” from which amphibians got their name. This
refers to animals that live part in water and part on land. Most lay small, shell-less
eggs surrounded by jellylike substance in moist places or in water. These hatch into
tadpoles with gills and tails. They lose the tail to develop lungs as well as legs and
Figure 23. Examples of unique bony fishes

261
move to land but close to water or damp habitats. They also have moist skin to help
the lungs for gas exchange while in dry land. Amphibians are divided into three
groups, the caecilians, salamanders, and frog and toads. Ceacilians live in water
or bury themselves in moist soil. Salamanders live in forest floors under rocks and
decaying logs.
Both frogs and toads jump. Some frogs can leap and attach to tree trunks
and branches. Toads are terrestrial and can even survive in hot places or desert.
Frogs have smooth skin while toads have rough or warty skin. Frogs and toads eat
worms, insects or small animals.
(Adapted from: Philippines. Department of Education. (2009). Science and Technology II. Textbook (Rev. ed.). Pasig City:
Instructional Materials Development Corporation. p. 302.)
Figure 24. Amphibians include (a) the mud puppy, (b) a tree frog,
(c) caecilian, and (d) toad
Q60. Refer to Figure 24. Which amphibian(s) is/are tail-less?
Q61. Which of them do not have legs?
Reptiles
Reptiles are animals that exhibit more adaptations for living on land. They lay
eggs with shells to protect them from drying. They also have smooth or rough scales
for protection from loss of body water.
(b)
(a)
(c)
(d)

262
Lizards and snakes have smooth scales. Examples of lizards are the house
lizard, gecko (tuko), monitor lizard (bayawak), chamleleon and horned toad. Snakes
are legless and have flexible jaws to enable them to swallow their prey whole. A
common snake species is the reticulated python seen in zoos. Poisonous species
include the cobra and the rattle snake. Snakes however, avoid people and do not
attack unless provoked or hurt.
Crocodiles and alligators are also reptiles. They are predators of fish,
deers, small cows or carabaos, and even attack humans. Alligators live in freshwater
and are only found in North and South America. Crocodiles live in fresh and salty
waters in tropical and subtropical regions. In the Philippines, two species are
present, the endemic Crocodylus mindorensis (Philippine Crocodile) and the
saltwater Crocodylus porosus. The Philippine crocodile is considered a critically
endangered crocodile species in the world.
Bodies of turtles and tortoises are enclosed in a shell. The head, legs and
tail are pulled inside this shell as protection from predators. Tortoises live on land
while turtles live mostly in water. Pawikan (marine turtles) live in the sea and females
come to shore only to lay eggs. There are species of marine turtles which are at
present in danger of extinction.
Birds
If reptiles are adapted to land life, most birds are adapted to fly.
Characteristics of birds that enable them to fly include: presence of wings and
feathers, large flight muscles in the breast bone and reduced weight. Birds weigh
less because their bones are light and hollow filled with air. Birds also have eggs with
shells and the legs are covered with scales. Their body temperature remains the
same despite varying environmental temperature due to the insulation provided by
feathers.
Birds have bills or beaks (Figure 25), and in coordination with the type of
wings and feet they have, are adapted to where they live and the kind of food they
eat.

263
Instructional Materials Development Corporation. p. 305.)
Figure 25 Different beaks of birds.
Q62. Examine the beak of the Philippine eagle. If it is for cutting, what do you think
does this bird eat?
Examples of birds that do not fly are the kiwi, penguin and ostrich.
Q63. Compare the legs of amphibians and reptiles with birds that you are familiar
with.
You often eat chicken during meals or even merienda. Or maybe balut and
salted eggs from ducks are your favourites! Snakes and big animals also prey on
smaller birds. You enjoy the relaxing chirping or singing of some birds and their
varied colors. Although certain birds feed on rice or corn grains, they have a role in
dispersing seeds to various places, resulting to perpetuation of many plant species.
The Philippine Eagle, which is found only in our country, has been declared
as a critically endangered species. It means that there is a possibility that the species
will disappear or be lost. The main reason is the loss of their habitat-- the forests --
due to logging and their conversion to farmlands.

264
Q64. If you live somewhere in eastern Luzon, Samar, Leyte or Mindanao where the
Philippine eagles specifically live, suggest ways to protect their habitat.
Mammals
Mammals differ from other animals because they have mammary glands that
produce milk to nourish their young and most have hair or fur. They breathe in air,
have four-chambered hearts and are warm-bloodied. Most of them also give birth to
live young and care for them.
The first group of mammals, called monotremes, lay eggs similar to those of
birds. The spiny anteater (echidnas) living in Australia, New Zealand and New
Guinea as well as the duck-billed platypus are monotremes (Figure 26).
(Source: Philippines. Department of Education. (2009). Science and
Development Corporation. p. 306).
Figure 26. Examples of Monotremes.
Marsupials or the pouched mammals also give birth to live young. After birth,
the young are kept inside pouches and are nourished with the milk from the
mammary glands within these pouches. Some marsupials are found in Central and
South America. The opossum lives only in North America. Others, such as the more
familiar koalas, kangaroos and wombats and flying phalangers, are found in Australia
and New Zealand.
The eutherians comprise the largest group of mammals. Known as the
placental mammals, they bear fully developed young inside the mother’s uterus.
These young are attached to the placenta through which they receive nourishment
until they are born. After birth, they continue to be cared for and nourished by milk
from the mammary glands. Table 2 presents the different groups of placental
mammals and their representatives.

265
Table 2. Placental mammals
Order Characteristics Examples
Insectivora insect-eating shrews, moles
Chiroptera flying bats
Rodentia gnawing rats, mice, squirrels
Lagomorpha rodentlike rabbits, hares
Edentata toothless armadillos
Cetacea aquatic whales, dolphins
Sirenia aquatic dugong, manatee
Proboscidea trunk-nosed elephants
Carnivora flesh-eating dogs, cats, bears, seals,
walruses
Ungulata hoofed foot horses, zebras, rhinoceros,
giraffes, carabaos, goats, pigs
Primates large brain relative
to body size
lemurs, monkeys, apes, humans
Pasig City: Instructional Materials Development Corporation. p. 307.)
Q65. Which of the eutherians live in water?
Q66. In your observation, how do humans differ from other primates?
Primates are the most highly developed of all animals. They are able to walk
erect, with fingers and toes adapted to grasp or hang on branches and hold things or
manipulate food. They also have a high degree of intelligence. Primates exhibit
social behavior like living in organized groups or communities. They take care of
orphaned individuals or even fight with competing groups. Scientists would like to
believe that the care given by females to their young contribute to their ability to
survive.
Q67. What characteristics differentiate mammals from other animals?
Mammals are present in various places, from the very cold to the warmest
regions and in salt waters. Many live among humans. Mammals have become an
important part of ecosystems. In grasslands, zebras eat plants and in turn are killed
and eaten by lions. In forests, bats eat insects and compete with monkeys for fruits.
Seeds are then spread for plants to grow in other areas. Wastes of these mammals
serve as fertilizers to plants. In human communities, rats carry bacteria and dogs
virus that cause diseases. In farmlands, carabaos work for people, while cows,
sheep and goats provide meat and milk. Rats destroy crops and compete with
humans for rice grains. In whatever way, good or bad, mammals affect the
ecosystems where they live.

266
You have just gone through all the different groups of organisms on Earth
known to science at present. You have learned about their similarities and
differences. The discussions and activities also showed how they are useful to one
another and the whole ecosystem or how some harm others.
Low and High Biodiversity
In the earlier grades you learned that among different ecosystems, the
rainforest has the highest biodiversity. This means that it has the greatest number of
species living in it. Rainforests have a high rainfall, thus, have lots of plants in them.
This condition provides shelter, water and food to many species that can survive
drought or disasters as well as competition with other species. This results to a
stable ecosystem with lesser rate of species loss. Tropical rainforests are located in
places near the equator, while temperate rainforests are found in the temperate
regions.
Q68. Based on the discussion above, how will you describe an ecosystem with low
biodiversity?
Activity 4
What is the importance of biodiversity to
ecosystems?
Objectives:
1. differentiate low from high biodiversity,
2. give advantages of high over low biodiversity,
3. identify ecosystems with low and high biodiversity, and
4. predict what will happen to an ecosystem with low biodiversity.
Materials Needed:
photos of different ecosystems
pencil/ballpen
Procedure:
1. Get photos of various ecosystems from your teacher.

267
2. Together with your groupmates, identify which of them have high or low
biodiversity.
Q69. Which ecosystem/s have high biodiversity? low biodiversity?
3. Study the photo below.
Photo by MD Sebastian
Figure 27. A banana plantation.
Q70. Does it have a high or low biodiversity?
Q71. What will happen if a pest will attack banana plants?
Q72. What will happen if a strong typhoon comes and heavy flooding occurs?
Q73. How will this affect the helpers and owner of the plantation?
4. Examine the photo below.

268
(Source: Philippines. Department of Education. (2009). Science and
Development Corporation. p. 339).
Figure 28. A coral reef ecosystem.
Q74. What biotic components are present in this ecosystem?
Q75. Describe some relationships and interactions that occur among these biotic
components.
Q76. Predict the effect of the presence of many crown of thorns sea star to the
ecosystem and its biotic components.
Q77. Why is high biodiversity advantageous over low biodiversity?
Q78. What is the importance of biodiversity to ecosystems?

269
The North Pole and certain deserts are examples of ecosystems with low
biodiversity.
Q79. Give other examples of familiar ecosystems with low biodiversity.
Protecting and Conserving Biodiversity
You have seen that organisms in an ecosystem are interdependent upon each
other for survival and harmonious existence. This interdependence among them
demonstrates the importance of biodiversity to an ecosystem. You must know
however, that as more species are discovered every year, others previously known
and identified have decreased in number or have disappeared. A good way to
remember the causes of species decline is through the acronym HIPPO*:
H - Habitat destruction
I - Invasion of introduced species
P - Population increase
P - Pollution
O - Overcollection/overharvesting of resources
Think of the biodiversity in your community at present. What would it look like
in the future?
In the following activity, you are going to make a list of conditions that you
want to see in your world in the future. Prioritize them, suggest ways and take action
to make them happen.
* Threats to Biodiversity. Retrieved from http://www.e-education.psu.edu/geog030/node/394
Activity 5
I create the future1
Objectives:
1. Make a personal and group vision for the future in relation to biodiversity
1
Adapted from Illinois Biodiversity Basics, a biodiversity education program of the Illinois
Department of Natural Resources, Chicago Wilderness, and the World Wildlife Fund

270
2. Analyze the different ways that government, groups, and individuals are
doing in order to arrive at the envisioned future, and
3. Take personal action towards conserving biodiversity.
Materials Needed:
copies of “Priority Pyramid” worksheet and “Making it Happen” handout for
each student and for each small group
pencil or ballpen
notebook or sheet of paper for the “future log”
Procedure:
Part I. My Future World
1. As a class, you are going to make a list of conditions that you want to see in
your world in the future and then, suggest ways and take action to make it
happen. Ask yourself this question: What do you want the future world to be?
What things or conditions do you want to see in the world, say, 50 years from
now? Make a list of at least five such conditions.
2. Be ready to share your ideas when your teacher will ask the class. Your
classmates will be sharing their ideas as well, so listen carefully. Your teacher
will write all the ideas on the board. Look at what visions of the future you and
your classmates have come up with.
Q80. What conditions do you and your classmates want to see in your future world?
3. Get a copy of the “Priority Pyramid” from your teacher. Complete this pyramid
with the conditions that you want your future world to have, ranking them from
the most important to the least. Write what for you is the most important
condition at the topmost box of the pyramid, the next two conditions on the next
level, and so on.
4. You will next share your personal pyramid in a small group. When it is your
turn, show your group your pyramid and explain how you chose your top three
conditions. When it is the turn of your groupmates to share, be sure to listen to
their explanations as well.
5. Now, discuss with your groupmates and create a group pyramid that will
represent your group’s priorities for the future. Each one should make a copy of
your group pyramid. Decide who among you will present to the class your
group’s top three priorities.
6. Compare your personal pyramid to the pyramid that your group came up with.

271
Q81. Why are there similarities and differences?
Q82. How do you feel about the final result, that is, the group pyramid?
Q83. How do you feel about the process you went through to come up with the
group pyramid?
Part II. Making it Happen
Q84. Will our dreams for the future come true by simply thinking about them?
1. Look at the different blocks (conditions) on your group pyramid. Are you
aware of anything that you or other people are already doing to ensure that
these will happen in the future? Make a list and discuss these with your
groupmates.
Q85. Do you know of any ongoing programs, initiatives and legislations related to
these priorities?
Q86. What government agencies, organizations, groups and individuals are
responsible for or are working on the conservation of biodiversity, either
locally or on a global scale?
2. Obtain a copy of the “Making it Happen” handout from your teacher. Read
about each of the projects and choose those that you think are making or will
make significant contributions to meeting the top three priorities in your group
pyramid. For each project that your group will choose, write a sentence or two
to describe ways it is working to achieve the identified priority. You can also
add what your group thinks as the project’s strongest and weakest points.
Part III. I Can Make a Difference!
Q87. What can you do to create a positive future?
1. Keep a “future log” for a week. Your log should list in bullet form, all your
activities, behaviors, speech and thoughts for each day. At the end of each
day, think about and write down how each bullet item affects the world
around you, either positively or negatively, and what consequences it could
have for the future.
2. Each day, add ways that you can do more to help preserve the earth’s
biodiversity.
Q88. What changes in your daily actions can you carry out to contribute to
conserving biodiversity?

272
Remember that the biodiversity found in your community, are what you need
to live and survive. As students, start right by taking seriously your learning and
understanding of your community’s biodiversity, the organisms’ importance to and
interactions with each other. Use them wisely and conserve biodiversity. It is only
when you understand all of these will you realize that you cannot afford to lose any of
these, for all of you and your future, will be affected. “ACT NOW, NO ONE CAN DO
THIS FOR YOU NOR FOR US!”
In the next module, you will be introduced to more ways by which these
organisms affect and interact with each other as well as with the environment they
live in.
Bailey, R. (2013). Three domain system. Retrieved from
http://biology.aout.com/od/evolution/a/99041708a.htm
Reece, J.B., Taylor, M.R., Simon, E.J., & Dickey, J.L. (2012). Campbell biology:
Concepts and connections (7th
ed.). Singapore: Pearson Education.
Karser, G.E. (2011). Classification: The three domain system. Retrieved from
http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit1/3domain/3domain.html.
Miller, K. R., & Levine, L. (2006). Prentice Hall biology. Upper Saddle River,
NJ:Pearson.
Strauss, E., & Lisowski, M. (1998). Biology: The web of life (Teacher’s ed.). Reading,
MA: Scott Foresman-Addison Wesley.
Philippines. Department of Education. (2009). Science and Technology II textbook.
(Rev. ed.). Pasig City: Instructional Materials Development Corporation.
Microbe Wiki. (n.d.). Methanospirillum hungatei. Retrieved from
http://mirobewik.kenyon.edu/index/.php/Methanospirillum_hungatei
Slime molds: Kingdom Protista. (n.d). Retrieved from
http://waynesword.palomar.edu/slime1.htm
Wikipedia. (2013). Giant tube worms. Retrieved from
http://en.wikipedia.org/wiki/Giant_tube_worm
http://www.allatsea.net/caribbean/sea-urchins-who-needs-them/
https://www.e-education.psu.edu/geog030/node/394 - United States
http://www.bbc.co.uk/news/science-environment-19800253

273
INTERACTIONS
Overview
In Module 1, you have learned about the diversity of organisms. Based on
the body structures and functions, organisms are classified using the hierarchical
taxonomic system (i.e. domain, kingdom, phylum, class, order, family, genus, and
species). Scientists use this system of classification to organize information and to
understand why living things exist the way they do in a particular environment. Also,
this helps us understand the role of each organism in the environment.
All these organisms need energy to sustain life. Every activity that organisms
do in ecosystems—breathing, moving, running, burrowing, growing—requires
energy.
The flow of energy is the most important factor that controls what kinds of
organisms live in an ecosystem. In this module, you will learn how organisms obtain
energy. This includes the discussion on how producers and consumers make
possible the flow of energy through ecosystems through food chains and food webs.
Students will then discover how the reduction in the amount of available energy limits
the number of steps that can occur in a food chain. Students will then identify the
role of bacteria in the cycling of some important elements or substances such as
water, oxygen, carbon and nitrogen.
How does energy become transferred from one organism
to another?
Unit 4
MODULE
2

274
In Grade 7, you have learned that plants, some kinds of bacteria, and algae
are capable of converting energy from the sun into chemical energy and store it as
chemical energy known as food. These organisms are called producers. The process
is called photosynthesis; it uses water, carbon dioxide, and sunlight.
Most plants make much more food each day than they need. Plants may
convert excess glucose into starch. Starch may then be stored in other parts of the
plants such as roots and fruits.
The stored energy is transferred to other organisms for their survival. When
people and other organisms eat plants, chemical energy from food substances is
transferred to their bodies. Energy moves from one trophic level to another. This
means that energy flows from one organism to another in the ecosystem.
Organisms that consume food for their energy supply are called consumers.
Q1. What raw materials from the environment are needed in the process of
photosynthesis?
Activity 1
How do you identify the components of a food
chain in an ecosystem?
Objectives:
1. distinguish between producers and consumers.
2. analyze the transfer of energy from one organism to another.
3. construct a food chain in a given ecosystem.
Materials Needed:
an article about “Monfort Bat Cave”
Activity sheet

275
Procedure:
1. Read an article about “Monfort Bat Cave.”
2. Read the following questions, and write your answer on the space provided.
Photo: Courtesy of Rodolfo S. Treyes, UP NISMED
The Island of Samal, part of Davao del Norte Province, is off the coast of
Mindanao. In this island is the Monfort Bat Cave which is approximately 245 feet
(75 meters) long and has five entrances. Bats cover 75 percent of its ceilings
and walls. An estimated 1.8 million bats, the largest known population of
Geoffroy’s rousette fruit bats in the world, are overloading Monfort Bat Cave on
the Philippines’ Samal Island.
Figure 1. Geoffroy’s rousette fruit bats clinging on walls
and ceiling of the cave.
Geoffroy’s rousette fruit bats feed on fruit and nectar. Their role as
pollinators and seed dispersers is essential in sustaining Philippine forests,
including such important commercial fruits as durian. Each bat consumes 11⁄2 to
3 times its body weight nightly in fruit and nectar. This colony could consume
550 tons (500,000 kilograms) of nectar from durian and other trees, pollinating
an incredible number of flowers.
Worldwide, cave-dwelling bats are in alarming decline due to human
disturbance and destruction of their cave roosts. In some areas, including Samal
Island, bats are captured and eaten by humans. Colonies like the one in Monfort
Bat Cave are now rare and in urgent need of protection. Their loss would
endanger the health of forests and human economies.
The bat’s colony should be able to survive natural predators – crows,
rats, 10-foot (3-meter) pythons and occasional monitor lizards – just as bat
populations do elsewhere. Untamed dogs and cats, however, also seem to do
bat hunting at Monfort Bat Cave.
© Bat Conservation International, www.batcon.org. Used with permission.
Photos courtesy of: Rodolfo S. Treyes, UP NISMED

276
Q2. What are the organisms found in the surrounding area of Monfort Bat Cave?
List them down in the table below.
Table 1. Organisms found in Monfort Bat Cave
Plants Animals
Q3. What group/s of organisms are considered as producers?
Q4. What part of the durian trees and other trees served as food for the bats?
Q5. The population of cave-dwelling bats is declining because they are being eaten
by other organisms. What are these organisms that feed on bats?
Q6. Among the organisms that feed on bats, are there organisms that possibly feed
on the predators of bats? ___ Yes ___ No
3. Divide the organisms into the following categories as shown in the table below:
Table 2. Categories of organisms living in the Monfort Bat Cave
Producers 1st
Order Consumer 2nd
Order Consumer

277
4. Based on Table 2, construct a food chain with at least 3 organisms
representing the producer, 1st
order consumer and 2nd
order consumer.
Producer 1st order consumer 2nd order consumer
Q7. You have just analyzed the transfer of energy by categorizing the organisms
according to their trophic level. In your own words, describe a food chain.
Food chains may be interconnected to form a food web. For example, one
kind of food may be eaten by several consumers. Or several foods may be eaten by
one consumer. A simplified food web in a Philippine forest is shown in Figure 2.
Figure 2. Interconnected food chains comprise this simplified food web
in a forest. Many organisms, including the decomposers, such as
bacteria and fungi are not shown in this food web.
Energy from
the Sun

278
Figure 3 shows a simplified food web in a marine environment. Microscopic
algae serve as the producers which are eaten by zooplankton. Zooplankton, in turn,
are eaten by small fish and other marine organisms.
Figure 3. Simplified food web in the sea illustrates the interconnected
feeding relationship between sea organisms.
The food web in Figure 4 includes a third group of organisms. Besides the
producers and the consumers, the food web shows the decomposers consisting of
bacteria and fungi. Decomposers act on dead organisms and change these to
simple nutrients which plants can use again.

279
Figure 4. The flow of food in this food web is from producers to consumers to
decomposers.
Q8. Without decomposers, will producers and consumers stay alive? Why?
Q9. Without producers, will consumers stay alive? Why?

280
Activity 2
Making food webs
Think of the food your family ate for supper last night. Make a food web
based on your meal. Remember, your food web must have producers, consumers,
and decomposers.
Q10. To which group of organisms do you belong?
Q11. Which trophic level do you occupy?
Food Pyramid
When organisms eat, they take in matter as well as energy into their bodies.
For example, when you eat chicken, the flesh of the chicken containing nutrients and
energy enters your body. You use the nutrients and energy to build muscles and
other parts of your body and to perform various activities.
The transfer of matter expressed as biomass and energy in food from one
trophic level to another are not one hundred percent used. Biomass is the total
mass of organisms in a food chain or a food web. Not all plants or animals at one
level are eaten by organisms at the next level. Some parts of plants or animals are
not edible, for example, wood, peel of some fruits, some seeds, shells, and bones.
In addition, much of the energy is lost as heat. Only about 10% of biomass and
energy are transferred to the next level. This relationship between producers and
consumers can be demonstrated through a biomass pyramid and an energy pyramid
(Figure 5). In the case of the marine environment, the source of energy in the food
chains is also the Sun.

281
Figure 5. The idealized pyramids of biomass and energy show losses at each
trophic level.

282
What do these pyramids demonstrate? A large amount of producers at the
base of the pyramid will be needed to support only a few of the consumers at the top.
The largest amount of biomass and energy are at the base of the pyramid. A
decrease or loss occurs at each succeeding level. As shown in Figure 5, 10 000 kg
of plankton that photosynthesize are needed to support only 1 000 kg of plankton
that do not photosynthesize. Planktons that photosynthesize are producers used as
food by the planktons that do not photosynthesize, the primary consumers. In turn,
1 000 kg of the primary consumers would support only 100 kg of small fish, which in
turn would sustain only 10 kg of lapu-lapu. At the highest level are humans. Note that
10 kg of lapu-lapu would sustain only 1 kg of the biomass of humans. Due to the loss
of biomass at each level, 10 000 kg of plankton at the base of the pyramid would
support only 1 kg of humans who are the top consumers.
In an energy pyramid the base of the pyramid is reduced and only 10%
moves to the next level. This loss goes on at every level until only 0.01% reaches the
top consumers.
Consider the food web in Figure 5. A food web can also fit into an energy
pyramid. It shows the flow of food through different organisms living in an area.
Construct an energy pyramid based on the food web. Include only the
producers and the consumers. Exclude the decomposers for a while.
Q12. Which group of organisms has the greatest biomass? Which has the greatest
energy?
Q13. Which group of organisms has the least biomass? Which has the least energy?
Q14. What happens to the amount of biomass from the bottom to the top of the
pyramid?

283
Activity 3
Meat eaters vs. plant eaters
What can you infer from the biomass pyramids below?
1. Study the following pyramid of biomass.
Figure 6. Pyramid of biomass
Q15. How much biomass of humans can 5 000 kg of corn support?
2. This time, study the following pyramid of biomass.

284
Figure 7. Pyramid of biomass
Q16. How much biomass of chicken can 5 000 kg of corn support?
Q17. How much biomass of humans can the chickens support?
Q18. Which is more efficient in converting biomass of producers to biomass of
consumers – a meat eater or a plant eater? Give your explanation.
Cycling of Materials in the Ecosystem
Materials in the ecosystem cycle constantly. This cycling of materials
includes the oxygen-carbon dioxide cycle, the water cycle, and the nitrogen cycle.

285
The Oxygen-Carbon Dioxide Cycle
Organisms use and produce gases in photosynthesis and respiration. These
gases flow through organisms and the environment in a cyclic process called the
oxygen-carbon dioxide cycle (Figure 8). The oxygen-carbon dioxide cycle shows
the interdependence among organisms for these important gases.
When plants photosynthesize, they use carbon dioxide and produce oxygen.
Oxygen produced by plants in photosynthesis is used by animals when they respire;
animals in turn produce carbon dioxide. Like animals, plants also carry out the
process of respiration. During respiration, plants use oxygen and produce carbon
dioxide.
Animals take in oxygen from the atmosphere and give off carbon dioxide
during respiration. This occurs day and night. Plants, however, give off oxygen and
take in carbon dioxide when they photosynthesize during the day. At night, when
plants are in darkness and cannot photosynthesize, they “breathe” just like animals.
They take in oxygen and give off carbon dioxide.
Notice that plants and animals depend on each other for these important
gases. Plants produce oxygen needed by animals. In turn, animals produce carbon
dioxide needed by plants.
Figure 8. Oxygen and carbon dioxide are continuously availed of by plants
and animals through the oxygen-carbon dioxide cycle.
Q19. What gas do plants produce that animals use?

286
Q20. What gas do animals produce that plants use?
The Water Cycle
Water circulates around the environment – the oceans, land, air and living
organisms. The cycling process involves evaporation, transpiration, condensation,
and precipitation. When solar energy warms the Earth’s surface, water evaporates
from the oceans, rivers, lakes and land. The escape of water through leaf pores
(transpiration) adds water vapor to the atmosphere. Upon cooling at higher altitude,
water vapor condenses and forms clouds. Eventually, precipitation occurs in the form
of rain or snow. On land, plant roots absorb water. In trophical rainforests, over 90
percent of the moisture is cycled through transpiration in plants. Some water seeps
downwards and replenishes the ground water. The excess eventually overflows into
the oceans and the water cycle continues
Figure 9. The Water Cycle.

287
The Nitrogen Cycle
About 79 percent of the gases in the atmosphere is made up of nitrogen gas.
Organisms use nitrogen to build proteins and nucleic acids. Some bacteria convert
nitrogen to ammonia. This process is called nitrogen fixation. Nitrogen-fixing
bacteria live in soil and are abundant in the nodules of legumes such as mung
beans.
The nitrogen cycle, shown in Figure 10, is a complex process with four
important stages.
Figure 10. The Nitrogen Cycle.

288
How do Human Activities Affect the Ecosystem?
Humans are the top consumers in many food pyramids. To increase food
production, they use methods that have an effect on food chains and food webs.
Some of the farming practices are described as follows:
Monoculture. This is the cultivation of a single crop in large areas. Vast
tracts of land are converted to rice farms, sugar farms, and coconut farms.
By limiting the cultivation of different kinds of plants, people also deprive
many animals of their food and home. These animals, some of which feed on insect
pests, move to other places. Only the insect pests that eat the monocrop remain in
the area. If uncontrolled, these pests can totally wipe out the monocrop in a short
time.
Some soil microorganisms depend on specific plants for food. Eliminating
these plants is harmful to the microorganisms. Since microorganisms are responsible
for returning plant nutrients to the soil, the cycling of nutrients for reuse of the plants
is disturbed.
Herbicides and Insecticides. Farmers spray their crops with insecticides to
kill insect pests, and with herbicides to kill weeds. However, the chemicals also
destroy other organisms, including beneficial insects and soil organisms which help
in decay.
Insecticides move up the food pyramid and accumulate in the body of
organisms. The smallest concentration of the chemical is at the base of the pyramid
occupied by producers. The amount increases towards the top. The greatest
concentration is found in the top consumers such as birds, mammals, and humans.
Many insect pests become resistant to chemicals. This may lead to the use of
increased amounts of pesticide.
Chemical Fertilizers. Monocrops usually require large amounts of chemical
fertilizers. Continuous and uncontrolled use of chemical fertilizers may increase soil
acidity, thus destroying soil structure. Findings show that more fertilizers are needed
for the same amount of yield after years of monoculture.
Fertilizers may run off to rivers, ponds, and lakes. Accumulation of fertilizers
may cause the death of these bodies of water.

289
Fertilizers in the water will cause increased growth of algae and other water
plants. They cover the water’s surface and block the passage of oxygen. Thus, less
oxygen is dissolved in water. Furthermore, when algae and aquatic plants die, decay
microorganisms use oxygen. Dissolved oxygen becomes insufficient, causing fish
and other aquatic animals to die.
Q21. Describe one way by which the following practices may disrupt a food chain or
food web:
1. monoculture
2. use of insecticides
3. use of fertilizers
To conserve the environment, some desirable practices are described below.
1. Grow a variety of crops instead of only one crop.
2. Use insects to fight other insects. This is known as biological control of insect
pests.
3. Instead of chemical fertilizers, try organic farming using natural fertilizers for
crops. Some natural fertilizers are compost and animal manure.
You may interview a farmer to get his or her opinion on these desirable practices.
Also ask if there are other good practices that the farmer uses in the farm.

290
References
Campbell, N.A., Reece, J.B., Taylor, M.R., Simon, E.J., & Dickey, J.L. (2012).
Campbell biology: Concepts and connections (7th Ed.). Pearson Benjamin
Cummings, USA: Pearson Education, Inc.
Department of Education, Culture and Sports. Instructional Materials Corporation.
(1990). Science and technology II: Textbook. Quezon City: Author.
Lantaw - Philippines Outdoor and Travel Photos. (2009). Retrieved from
http://www.lantaw.com/2009/10/samal-monfort-bat-cave.html
Locke, R. (2006). A treasure trove of fruit bats. BATS Magazine, 24(4). Retrieved
from www.batcom.org/pdfs/batsmag/batswinter06.pdf.
Education Development. (n.d.). Nitrogen cycle [Poster]. Quezon City:
Author.
Education Development. (n.d.). Water cycle [Poster]. Quezon City: Author.

291
THE DIGESTIVE SYSTEM
Overview
Food plays a central role in the survival of species. Food gives organisms
energy that enables them to carry out the many activities they do each day; this
includes predators chasing a prey or a prey escaping a predator, arboreal organisms
climbing trees to gather fruits, or fish swimming in schools in search for food, to
name a few. Organisms are able to obtain energy from the foods they eat through
digestion.
Digestion of food is carried out by the organs and substances of the
digestive system. During digestion, food is broken down to smaller parts -- a fraction
of which is made up of nutrients. These nutrients are circulated to the different parts
of the body through the bloodstream and assimilated by cells.
Almost all animals have a digestive system in which food enters the mouth,
is moved through a long tube, and exits the anus as feces. The food is broken down
into soluble molecules and is moved rhythmically by the smooth muscle in the walls
of the digestive organs.
Different species of organisms have different ways of digesting their food. In
humans, digestion starts in the mouth where food is chewed and broken down to
smaller pieces for easier digestion. This is called mechanical digestion. Initial
chemical digestion starts also in the mouth. This is carried out by enzymes --
molecules that speed up chemical reactions. Enzymes present in saliva such as
amylase helps break down carbohydrates, which are large complex molecules, into
simpler ones that can be used by the body.
Unit 4
MODULE
3

292
After swallowing, the food -- now turned into a bolus -- enters the esophagus
(gullet) and is moved down into the stomach where it mixes with gastric juices and
acids. Other enzymes such as protease and lipase help break down proteins in the
stomach and fats in the small intestine, respectively. Digestion ends in the small
intestine where nutrients are absorbed in the villi and enter the circulatory system.
Wastes that remain after digestion go to the large intestine where water is also
reabsorbed. These wastes, including the water that was not reabsorbed, are
temporarily stored in the rectum before they are excreted out of the body through the
anus.
Digestion in other organisms works similarly. However, there are specialized
structures found in some species that perform special digestive functions.
This module introduces you to the different organs that make up the digestive
system of animals and how they interact with each other to digest food and nourish
their bodies. Emphasis is given on the human digestive system and its processes.
Activity 1
Part 1A. A gutsy game
Objectives:
1. identify the organs that make up the digestive system; and
2. describe the function of each organ.
Materials Needed:
game board (refer to following page)
a piece of die
tokens or playing pieces
How does the digestive system break down food to
nourish the body?

294
Procedure:
1. Find a classmate with whom you can play the board game.
2. Choose a token for you and your classmate; place the tokens on the board’s
starting line.
Q1. The game you are about to play is an analogy of the digestive system.
What do the tokens represent?
3. Take turns rolling the die.
4. The number on the die determines how many spaces you will move your token.
Q2. What do the spaces on the board game represent?
5. Follow the directions -- if there is any -- on the space you land your token.
Q3. What do the directions on some of the spaces tell you about the digestive
system?
6. The player who first makes it all the way through the digestive system and
down to the finish line wins the game.
In Activity 1, you should have inferred that the digestive system is made up of
different organs that work together to break down food and nourish the body.
Describe the illustrations on the board game. What do these illustrations represent?
What do the spaces or boxes drawn on the board game represent?
Notice that the board game is just an analogy of the structures of the
digestion system and the processes they carry out. Refer to Figure 1 to compare the
illustrations on the board game with the actual structures or organs of the digestive
system.
Are these structures also found in other organisms? Are these structures in
the digestive system of humans the same as those found in other organisms? Do
they serve the same or similar functions?

295
Figure 1. The human digestive system.
The digestive systems of animals and the organs that make them up vary
across species. Some structures like the rumen, crop, and gizzard are found only in
some species. The rumen is common among ruminants that include the goats, cows,
and carabaos. What do you think is the function of this structure? The crop and
gizzard are found in birds and some species of invertebrates like the grasshoppers
and earthworms. What functions do you think do these structures perform in
digestion?

296
Almost all animals have a tubelike digestive system; one end of the tube
serves as the mouth while the other end serves as the anus. This digestive system is
called a Complete Digestive System. Food enters the mouth, passes through the
long tube, and exits as feces through the anus.
The smooth muscles of the tubelike digestive organs move the food
rhythmically through the system where it is broken down into absorbable forms.
Outside of this tube are attached some accessory organs -- the liver, gall bladder,
and pancreas -- which also help in the digestion of food. Figure 2 shows a
comparison of the digestive systems of different representative species of animals.
Figure 2. Digestive tracts of different representative species of animals.

297
Q4. In what ways are the different digestive systems of animals similar? In what
ways are they different?
The more primitive animals like the Hydra have a ‘digestive system’ with
only one opening (see Figure 3) which is also called an Incomplete Digestive
System. These organisms eat and defecate with their mouth which also alternates
as their anus!
Activity 1
Part 1B. A sweet break!
Objectives:
1. describe the process of mechanical digestion; and
Figure 3. Hollow body of Hydra. The animal takes in food, digests food in its
digestive cavity, and removes wastes through its mouth. Also shown is an
enlarged part of the body wall.

298
2. explain how the physical breaking down of food helps in its digestion.
Materials Needed:
two 100 mL beakers or clear containers
warm water
two pieces of candies (hard candies)
mortar and pestle
paper towel
Procedure:
1. Fill the two beakers with warm water. Make sure that the amount of water placed
in each glass is about the same. Label the glasses A and B.
2. Prepare two pieces of candies. Wrap a piece of candy in a paper towel and crush
it using a mortar and pestle or any hard object like a piece of wood.
3. Place one piece of candy into the glass of warm water labeled A and place the
crushed pieces of candy in the remaining glass of warm water labeled B.
4. Observe how long it takes for the whole candy in Glass A and the crushed pieces
of candy in Glass B to dissolve.
5. Record your observation.
Q5. How does crushing the candy to smaller pieces affect its dissolution?
Q6. What does crushing the candy represent in the process of digestion?
Activity 2
How do enzymes affect digestion?
Objectives:
1. explain how enzymes affect digestion; and
2. infer chemical changes in food as it undergoes chemical digestion.

299
Materials Needed:
1 tablespoonful of granulated gelatin
10 mL fresh pineapple juice
10 mL bromeliad leaf juice
water
measuring cup
spoon
100 mL graduated cylinder
3 droppers
3 test tubes
test tube rack
markers
hot plate
Procedure:
1. Number and label the test tubes (1-water, 2-fresh pineapple juice, and 3-
bromeliad leaf juice).
2. Prepare one tablespoonful of granulated gelatin in the measuring cup using 100
mL of boiling water.
3. Stir well with a spoon until the gelatin is dissolved.
4. Place 3 mL of water into test tube 1, 3 mL of fresh pineapple juice into test tube
2, and 3 mL of bromeliad leaf juice into test tube 3.
5. Add 10 mL of gelatin mixture to each test tube. Shake well to mix thoroughly.
6. Refrigerate the samples overnight.
7. On Day 2, check the contents of each test tube for solidification of the contents.
Record your observations.

300
Table 1. Effect of enzymes on digestion
Test Tube Contents How do the contents of the test tube
look like on Day 2?
1 Water and gelatin
2 Fresh pineapple juice
and gelatin
3 Bromeliad leaf juice and
gelatin
Food undergoes physical and chemical change as it moves from one part of
the gastrointestinal tract to the other. Digestion makes the nutrients found in food
available to the different parts of the body for the organism’s nourishment and overall
wellness. In Activity 2, an enzyme called bromelain which is present in fresh
pineapple juice and in bromeliad plants is used to demonstrate digestion of proteins.
Q7. How did bromelain affect the protein in gelatin?
Q8. Which of your observations show this effect?
Q9. There are other kinds of enzymes in your digestive system. How do these
enzymes affect digestion?
Bromelain refers to a group of enzymes from bromeliad plants that break
down proteins. They are proteases. Bromelain is found in both fresh pineapple and
bromeliad leaf juices. This should not come as a surprise because pineapple is a
bromeliad plant.
_____________________________________________________________________
At certain times of the day, you hear your stomach rumbling. This is the
sound you hear as the gastric juices are churned in an empty stomach. This
indicates that you are already hungry and it is time for you to eat. The stomach and
some glands start to produce gastric juices to prepare your stomach for the food you
will eat. These gastric juices provide an acidic environment in the stomach. How do
these gastric juices affect digestion in the stomach? In Activity 3, you will be
introduced to the effect of pH on the digestion of food in the stomach and the
intestine.

301
Activity 3
How does pH affect enzyme activity?
Objectives:
1. describe the process of chemical digestion; and
2. explain how enzymes act as catalyst during digestion.
Materials Needed:
1 tablespoonful of granulated gelatin
10 mL fresh pineapple juice
water
measuring cup
spoon
3 droppers
3 test tubes
test tube rack
markers
hot plate
1 M HCl
1 M NaOH
Procedure:
1. Label the test tubes (A – acid, B – base, C – control <water>)
2. Prepare one tablespoonful of granulated gelatin in the measuring cup using
100 mL of boiling water.
3. Stir well with a spoon until the gelatin is dissolved.
4. Place 3 mL of pineapple juice into each of the labeled test tubes. Transfer 1 mL
each of HCl, NaOH, and water into the corresponding test tubes of pineapple
juice.
TAKE
CARE!
Do not get
any acid or
base on your
skin.

302
5. Transfer 10 mL of gelatin mixture to each test tube.
6. Using a spoon, stir the gelatin well until it dissolves completely.
7. Refrigerate the test tubes overnight.
8. On day 2, observe the contents of each test tube. Record your observations.
Table 2. Effect of pH on enzyme activity
Test Tube Contents
How do the contents of the test tube
look like on Day 2?
A Acid added on gelatin
with pineapple juice
B Base added on gelatin
C Water added on gelatin
(Control)
What is chemical digestion? Where does chemical digestion take place in the
human digestive tract?
Q10. What role do the digestive enzymes have in digestion?
Q11. In which test tube did you observe the greatest amount of protein digestion?
Q12. In which test tube did you observe the least amount of protein digestion?
Q13. How do you explain your results?
Q14. Did your results support your hypothesis? Explain your answer.
Q15. In the human digestive tract, where is protein digested chemically?

303
Carbohydrates are broken down to simple sugars that are absorbed in the
small intestines; they are circulated to the different parts of the body as they join the
bloodstream. They are used up as sources of energy once they are assimilated by
the cells; those that are circulated into the liver are stored.
Proteins are broken down to their component parts -- also called amino acids
-- in the stomach. This process is aided by acids secreted by the cells that make up
the walls of the stomach and enzymes that are present in the gastric juice. Like the
simple sugars, amino acids are absorbed in the small intestine through the villi -- the
fingerlike structures that line the walls of the small intestines -- and circulated to the
different parts of the body. Those that are circulated into the liver are stored as
glycogen.
In the case of fats and lipids, their digestion is completed in the small
intestine where bile secreted from the liver disintegrates them into fatty acids and
glycerol – particles that are circulated to the rest of the body and stored in fatty
tissues.
Activity 4
A journey into the digestive system
Objectives:
1. Infer how the organs of the digestive system work together to carry out
digestion of food and assimilation of nutrients; and
2. explain what happens to food as it gets digested.
Materials Needed:
Video clip: Journey of the digestive system
Link: http://www.youtube.com/watch?v=e3O1AdlC8bI
Writing materials

304
Procedure:
1. Your teacher will show a movie clip titled, Journey of the Digestive System.
2. Take down notes as you watch the movie clip.
3. On a separate sheet of paper, answer the following questions.
Q16. What does the movie clip say about the digestion of food?
Q17. What changes happened to the food as it was moved through the digestive
tract?
Summary
Digestion starts when
food is taken into the mouth.
This is called ingestion. As you
chew, you are breaking the food
into small pieces as a means of
mechanical breakdown. The
pieces mix with saliva before you
swallow. Saliva is a watery liquid
made by the salivary glands. It
softens and wets the food in the
mouth and also initially starts
chemical digestion through the
enzymes present in it. Then the
food passes through the
esophagus. Muscle contractions
in the esophagus help move the
food down to the stomach. This
process is called peristalsis
(see Figure 4). Figure 4. Peristalsis in the esophagus.

305
Stomach juices are chemicals made by the body that help digest food. The
stomach is made up of muscles that churn and help mix the food and break it into
even smaller pieces.
The digestive glands in the stomach lining produce acids and enzymes that
digest proteins. These digestive juices could, in fact, harm the stomach. However, a
thick mucus layer helps keep this acidic chemical environment from destroying the
tissues of the stomach.
Digested molecules of food are absorbed through the small intestine. The
walls of the small intestine contain many folds that are lined up with tiny fingerlike
protrusions called villi. These villi are in turn covered with even smaller protrusions
called microvilli. These structures increase the surface area through which nutrients
are absorbed. During absorption, these nutrients pass through the walls of the
intestine and into the bloodstream where they get transported to the different parts of
the body.
The undigested parts of food or those that were not absorbed by the body are
eliminated as feces. This process is called elimination or defecation. Figure 5 shows
how food is changed to soluble forms as it is moved from one part of the digestive
system to another.
Figure 5. The process of digestion.

306
References
Beckett, B. & Gallagher, R. (2001). Modular science: Biology. Oxford: Oxford
University Press.
Goldsmith, I. (1969). Human anatomy for children. New York: Dover Publications.
Guyton, A. (1964). Function of the human body. Philadelphia: W. B. Saunders.
Ravielli, A. (1963). Wonders of the human body. New York: The Viking Press.
VanCleave, J. (1995). Jan VanCleave’s the human body for every kid: Easy activities
that make learning science fun. New York: John Wiley.
Links
Beacon Lesson Plan Library. (n.d.). You are what you eat. Retrieved from
http://www.beaconlearningcenter.com/Lessons/2719.htm
Digestive disorders. (2013). Retrieved from http://www.nutrition.gov/nutrition-and-
health-issues/digestive-disorders
Eat right. (1997). Retrieved from
http://www.eduplace.com/rdg/gen_act/cooking/eatrigh.html
Healthy or not healthy? (1999-2010). Retrieved from http://www.teachnology.com/
teachers/lesson_plans/health/healthyornot35.html
National Geographic. (1996-2013). Your body’s fuel factory. Retrieved from
http://science.nationalgeographic.com/science/health-and-human-
body/human-body/digestive-system-article.html
National Geographic Channel. (2010). Journey of the digestive system. Retrieved
from http://www.youtube.com/watch?v=e3O1AdlC8bI
Nutrition games and activities. (n.d.). Retrieved from
http://www.wartgames.com/themes/nutrition.html
Ward, V.L. (n.d.). A walk through the gut. Retrieved from
http://www.accessexcellence.org/AE/AEC/AEF/walk.php

307
NUTRITION AND
WELLNESS
Overview
In the previous module, you have explored how the body obtains the nutrients
it needs to fuel its activities. In addition to providing energy, our diet must also
supply the raw materials needed for building complex molecules the body needs to
grow, maintain itself, and reproduce.
In this module, you will survey the nutritional requirements of our body. This
module will discuss nutrition and consider the choices we make that affect the proper
functioning of the digestive system. This module will also consider how our diet and
lifestyle contribute to the functioning of the human body as a whole.
Your body needs food for energy, growth and repair, and as a source of
substances for body processes. Different types of food provide different nutrients.
How do you know if you are getting the right kind and amount of nutrients from the
food that you eat?
What are the nutritional needs of our body?
What happens when the body’s nutritional needs are not
adequately met?
Unit 4
MODULE
4

308
Activity 1
Am I eating right?
Objectives:
1. make a record of your daily meals, and
2. determine if your food intake adequately meets nutritional requirements.
Procedure:
A.
1. Record in a Daily Meal Journal what you eat for three days. Table 1 shows a
sample meal record for one day.
Table 1. Sample daily meal journal
Date Meal Food and Beverage Amount
June 15 Breakfast Rice 1 cup
Tinapa 1 pc
Fried egg 1 pc
Water 1 glass
Snack Pandesal 2 pcs
Water 1 glass
Lunch Rice 1 cup
Ginisang munggo 1⁄2 cup
Water 1 glass
Snack Boiled banana 1 pc
Water 1 glass
Dinner Rice 1 cup
Fried galunggong 1 pc
Kamote tops 1⁄2 cup
Water 1 glass

309
2. Interview your school nutritionist, school nurse, or barangay health worker on
the kind and amount of food that you should eat to meet your nutritional
requirements.
You should have gathered from your interview that you need to eat a variety
of foods since no naturally occurring food has every nutrient. The Food and Nutrition
Research Institute (FNRI) has developed a food pyramid for Filipinos, a simple and
easy to follow daily eating guide. This guide is useful in helping people select food
that supply all the nutrients for energy and growth.
Figure 1 shows a food pyramid which illustrates the recommended dietary
allowance for teenagers.
Figure 1. The Food Pyramid for teenagers recommends eating a variety of
foods to ensure that all nutrients are provided in proper amount and balance.
Source: Food and Nutrition Research Institute, Department of Science and
Technology

310
Foods that contain the same type of nutrient belong to a food group. Foods
have been divided into five groups – a) rice, rice products, corn, root crops, bread,
noodles; b) fruits and vegetables; d) milk and milk products, eggs, fish, shellfish,
meat and poultry, dried beans and nuts; and e) sugar and sweets, fats and oil. The
recommended daily amount for each food group will supply your body with the
nutrients it needs for good health.
3. Compare your entries in your daily meal journal with the recommended daily
amount of servings.
An accurate meal journal tells a lot about your eating patterns. The Daily Meal
Journal below belongs to a fourteen-year old named Conrad. Study his meal journal
and answer the questions that follow.
Daily Meal Journal
Date Meal Food and Beverage Amount
June 15 Breakfast Rice 1 cup
Tuyo 1 pc
Water 1 glass
Snacks Yema 3 pcs
Lunch Rice 1 cup
Fried tilapia 1 pc (medium)
Water 1 glass
Dinner Rice 1 cup
Fried chicken 1 pc
Water 1 glass
Q1. Which food group in the Food Pyramid do you observe the greatest number of
servings?
Q2. What did Conrad eat that belong to this food group?
Q3. Which food group/s do you see no servings?
Q4. Based on the Food Pyramid, how many servings from that group should
Conrad have eaten?

311
Q5. What should Conrad include in his meals to ensure that he gets all the nutrients
indicated in the Food Pyramid?
Daily Servings
For each day you should eat six to eight servings from the rice and rice
products group, three servings from the vegetable group, three servings from the fruit
group, one glass from the milk group, and two and a half servings from the fish and
meat group. Only small amounts of sweets, fats, and oils should be consumed.
The size of a serving is different for different foods. For example, one cup of
rice or 5 pieces of small pandesal is equivalent to one serving of the rice and rice
products group. One piece medium-sized fish or 1/3 cup cooked dried beans is
equivalent to one serving of the fish, meat and beans group. The table below shows
the food groups, recommended intake, and equivalent of one serving portion of
common foods.
Table 2. Food groups and the equivalent of one serving portion of common foods
Food groups Recommended intake Equivalent of one (1) serving portion of
common foods
Fat and oils 6-8 teaspoons
1 teaspoon coconut oil (5 grams)
= 1 tablespoon coconut cream
= 1 teaspoon mayonnaise
= 1 teaspoon margarine/butter
= 2 teaspoons peanut butter
Sugar/sweets 5-6 teaspoons
1 teaspoon sugar (5 grams)
= 1 teaspoon honey
= 1 teaspoon fruit flavored drink
(powder)
= 2 teaspoons jam/jellies/preserves
= 1/5 glass softdrink/flavored drink
= 2-3 teaspoons fruit flavored drink
(concentrate)
= 1 piece hard candy
Fish, shellfish,
meat & poultry,
dried beans and
nuts
2 1⁄2 servings
1 serving
= 1 piece medium size fish
= 1/3 cup shellfish, shelled
= 3 centimeters cube cooked pork/
beef/chicken
= 1/3 cup cooked dried beans/nuts
= 1⁄2 cup tofu
= 1 piece tokwa
= 1 slice cheese

312
Egg 1 piece 1 piece chicken egg
Milk and milk
products
1 glass
1 serving
= 1 glass whole milk
= 4 tablespoons powdered whole
milk diluted to 1 glass of water
= 1⁄2 cup evaporated milk diluted to
1⁄2 glass of water
Vegetable 3 servings
1 serving of leafy vegetables
= 1 cup raw or 1⁄2 cup cooked
1 serving of other vegetables
= 1⁄2 cup raw or 1⁄2 cup cooked
Fruits 3 servings
1 serving of vitamin C rich food
= 1 medium sized fruit or 1 slice of
a big fruit
1 serving of other fruits
= 1 medium sized fruit or 1 slice of a
big fruit
Rice, rice
products, corn,
root crops, bread,
noodles
6-8 servings
1 serving
= 1 cup rice
= 4 slices loaf bread
= 2 slices puto
= 5 pieces small pandesal
= 1 cup corn
= 2 cups noodle
= 1 cup cooked yellow kamote
Take Home Activity:
1. Gather data on what local produce are available in your province and two
nearby provinces. Research on the nutritional value of these local produce.
2. Tabulate the locally available food according to the categories in the Food
Pyramid. Try to use local food produce in planning your meals.
Fiber
Although fiber cannot be digested and absorbed by the body, it plays an
important role in cleaning the digestive tract. Fiber absorbs water and helps
eliminate the waste products of the body. Fiber may help prevent certain diseases
such as heart disease, cancer and diabetes. Not eating enough fiber can cause
constipation and other intestinal problems. You should have just enough fiber in your
diet as eating too much fiber can cause nutrients to pass through the system too
quickly to be absorbed. Examples of some food that are rich in fiber are grains,
fruits, and vegetables.
Source: http://www.fnri.dost.gov.ph

313
Water
Your body is made up of 55 to 60 percent water. Water plays important roles
in important processes such as digestion, elimination of waste products, and
regulation of body temperature. You need to drink about 8 glasses of water a day to
replace the amount you lose through sweat, urine, and respiration.
Food Plate
Another tool in helping you monitor what you eat is the food plate (Figure 2).
It is recommended that you should divide your food plate into four parts – the first
part for grains like rice, corn, or bread, the second part for fruits, the third part for
vegetables, and the fourth part for protein like meat or fish. Since vegetables differ in
nutrient content, it is recommended that you eat a variety of vegetables each day.
The most important thing to remember is to fill one-half of your plate with fruits and
vegetables.
Figure 2. The Food Plate is divided into four
parts as a general guide for how much a
person should choose from each food group.

314
Activity 2
What happens when nutritional needs are not
adequately met?
A good diet is important for proper growth and development and for the
prevention of disease. A number of health problems and diseases are caused by a
poor diet.
Objectives:
1. analyze the consequences of an unhealthy diet.
2. demonstrate understanding of diseases that result from nutrient
deficiency and their prevention and treatment.
Procedure:
1. Using the table below as a guide, research on the sources of carbohydrates,
protein, fats, vitamins and minerals, the functions of these nutrients, and the
health problems that result when the requirement for these nutrients are not
adequately met.
Nutrients Food Sources Functions
Deficiency signs and
symptoms
Carbohydrates
Protein
Fats
Vitamins and
Minerals

315
2. Present your output to the class.
Insufficient intake of nutrients can cause nutrition disorders. These disorders
may cause health problems, especially in children, which may hinder growth and
development.
Activity 3
Using essential concepts in nutrition to planning
a menu
Objectives:
1. design a three-day menu that reflects balanced meals and provides the
recommended daily allowance to an active teenager, and
2. incorporate local produce in your menu.
Procedure:
1. Design a three-day menu that reflects balanced meals and provides the
recommended daily allowance to an active teenager.
2. Incorporate locally produced food products in your menu.
3. Present your output to the class.
Eating a variety of food increases the probability of getting the necessary
nutrients that your body needs. Getting enough nutrients will result to proper growth
and development and prevention of health problems. Learning how to meet your
nutritional needs by making good food choices will help you become healthy.

316
References
Daily Nutritional Guide Pyramid for Filipino Children (13-19 years old). Retrieved
from: http://www.fnri.dost.gov.ph/index.php?option=content&task=view&id=1676
Philippines. Department of Education. (2009). Science and Technology II textbook.
(Rev. ed.). Pasig City: Instructional Materials Development Corporation.
Philippines. Science Education Center. (1971). Plants of the Philippines (2nd
ed.).
Quezon City, Philippines: Pundasyon sa Pagpapaunlad ng Kaalaman sa
Pagtuturo ng Agham, Ink.

317
CELLULAR
REPRODUCTION AND
GENETICS
Overview
When you look at your parents, you can see features that you share with
them, such as the shape of the eye, the presence of dimples, or even the hand you
use when you write. The sharing of features can be explained by heredity, where
traits are passed on from parents to offspring. Yet when you look at your brothers
and sisters, even if you share the same parents, each one of you can be considered
unique based on the combination of traits each possesses. That is variation, which
demonstrates differences among individuals.
Genetics is the study of heredity and variation. It aims to understand how
traits can be passed on to the next generation and how variation arises.
Every living thing undergoes reproduction. The nutrients taken by an
individual will provide for energy for metabolic processes, for growth and
development as well as reproduction. The cellular level of reproduction, in the form of
cell division, provides for the backdrop for the organismal level of reproduction.
This module will differentiate the two types of cell division, mitosis and
meiosis, as well as correlate heredity with the behavior of the chromosomes in the
cell during meiosis. Investigations are included that will help you understand the
mechanisms of heredity and the expression of traits.
What are the different types of cell division?
How are traits passed on to the next generation?
Unit 4
MODULE
5

318
The Chromosome
All living things contain what we call the genetic material that serves as the
set of instructions that direct the activities and functions of the cells. These genetic
materials, also known as the deoxyribonucleic acid or DNA, are passed on from
one generation to the next to ensure the continuity of life. In eukaryotic cells (cells
with organelles), the DNA are bound with proteins and are organized as beads on
strings to form chromosomes (Figure 1).
Figure 1.The organization of the DNA as genetic material.

319
The number of chromosomes in a cell is characteristic of the species to which
it belongs. For example, humans have 46 chromosomes while rice have 12. Table 1
summarizes the chromosome numbers of some common organisms.
Table 1. Chromosome numbers of selected organisms.
Organism Chromosome number
Saccharomyces cerevisiae
(common yeast)
32
Caenorhabdites elegans
(roundworm)
12
Drosophila melanogaster
(fruit fly)
8
Canis lupus familiaris
(dog)
52
Homo sapiens
(man)
46
Arabidopsis thaliana
(mouse ear cress)
10
Oryza sativa
(rice)
24
Zea mays
(corn)
20

320
The Cell Cycle
The chromosomes of a cell change form as the cell transitions from one
stage to another in a typical cell cycle. The cell cycle may be divided into two stages:
the interphase where the chromosomes are long and extended and are also
referred to as chromatin, and the cell division phase where the chromosomes
become condensed or thickened (Figure 2).
Figure 2. The cell cycle.
The interphase refers to the period that follows one cell division and precedes
another. During this stage, the cell does not divide; it merely grows. The
chromosome doubles or replicates itself because the DNA molecule contained in the
chromosome produces an exact copy of itself.
The interphase is divided into three substages. The stage from the formation
of a new cell until it begins to replicate its DNA is called the first gap period or G1,
during which time the cell grows initially. This stage is characterized by protein and
ribonucleic acid (RNA) synthesis. RNA, which is synthesized based on the DNA, is
then used to synthesize proteins.

321
The middle stage of interphase, called the synthesis stage or S, is the period
of DNA synthesis or replication. The chromosomes are duplicated in preparation for
the next cell division. The second gap period or G2, falls between the S period and
the next cell division or M (mitosis or meiosis, see discussion below) phase. G2
represents a period of rapid cell growth to prepare for cell division.
During interphase, the nucleus is clearly visible as a distinct membrane-
bound organelle. In stained cells, this membrane can be clearly seen under the light
microscope. One or more nucleoli are visible inside the nucleus. On the other hand,
the chromosomes cannot be clearly seen. They appear as an irregular mass that is
grainy in appearance because the DNA they contain are stretched out thinly in the
nucleus. This facilitates the replication of DNA during the S phase.
Cell Division
Alternating with the interphase is the cell division phase. In eukaryotic cells,
there are two types of cell division: mitosis and meiosis.
1. Mitosis
This type of cell division produces two identical cells with the same number of
chromosomes. Mitosis is divided into four stages.
STAGE A: Prophase. The nuclear membrane and nucleoli may still be present. The
chromosomes are thicker and shorter because of repeated coiling. At this stage,
each chromosome is made up of two identical sister chromatids as a consequence
of replication of DNA during the S phase. The two chromatids produced from one
chromosome are still attached at one point, called the centromere. The centromere
may divide the chromosome into the shorter arms, also called the p arms (‘p’ stands
for petite in French) and the longer q arms. If the chromosomes are stained using
Giemsa, alternating dark and light regions will appear. These are the
heterochromatin and euchromatin, respectively. The heterochromatin are more
coiled and dense than the euchromatin (Figure 3).

322
Figure 3. Parts of the chromosome.
STAGE B: Metaphase. The nuclear membrane has disappeared while the highly
coiled chromosomes align at the metaphase plate, an imaginary plane equidistant
between the cell’s two poles. Spindle fibers are also formed. Each fiber binds to a
protein called the kinetochore at the centromere of each sister chromatid of the
chromosome.
STAGE C: Anaphase. The paired centromeres of each chromosome separate
towards the opposite poles of the cells as they are pulled by the spindle fibers
through their kinetochores. This liberates the sister chromatids. Each chromatid is
now regarded as a full-fledged chromosome and is only made up of one sister
chromatid.
STAGE D: Telophase. The chromosomes are now at the opposite poles of the
spindle. They start to uncoil and become indistinct under the light microscope. A new
nuclear membrane forms around them while the spindle fibers disappear. There is
also cytokinesis or the division of the cytoplasm to form two separate daughter cells
immediately after mitosis.

323
Activity 1
Observing mitosis
Objectives:
After you have performed this activity, you should be able to:
1. identify the different stages of mitosis in plant and animal cells, and
2. differentiate plant and animal mitoses.
Materials:
Prepared slides of onion root tip and white fish blastula
Compound microscope
Procedure:
1. Examine the onion root tip and white fish blastula slides under the microscope.
Based on the descriptions provided in the previous section, identify and draw
from each slide the following: interphase, prophase, metaphase, anaphase,
and telophase. Cells do not divide at the same time. Therefore, you will find
cells at different stages of mitosis. With the LPO, locate and study the cells at
these stages, then switch to the HPO to study the chromosomes in detail.
2. Locate the centrioles at opposite sides of a mitotic cell. These form star-like
structures called asters at the poles of the spindles.
Q1. Where can you find these centrioles, in plant cells or animal cells?
3. Detect the presence of cleavage furrows in the mitotic cell of the white fish
blastula. Cleavage furrows grow inward in the cell membrane until the cell is
divided into two.
Q2. Do you also find a cleavage furrow in mitotic plant cells?
_____________________________________________________

324
2. Meiosis
The number of chromosomes normally remains the same within the species.
It does not double or triple for every generation. This suggests that a different kind of
cell division must take place in an individual. This kind of cell division is called
meiosis, from a Greek word which means “to make smaller.” Meiosis reduces the
chromosome number in half. It takes place in plants and animals whenever
gametes, or sex cells, are formed through the process called gametogenesis.
Meiosis is a special type of cell division where the cell undergoes two rounds
of cell division to produce four daughter cells, each with half the chromosome
number as the original parent cell and with a unique set of genetic material as a
result of exchange of chromosome segments during the process of crossing over.
The first round of meiotic division, also known as meiosis I, consists of four
stages: prophase I, metaphase I, anaphase I, and telophase I. Prophase I of
meiosis I, unlike its counterpart in mitosis, is more elaborate and should be
understood well in order to grasp the mechanisms of heredity.
STAGE A: Prophase I. Meiosis starts with this stage and includes the following sub-
stages:
Leptotene. Each chromosome is made up of two long threads of sister chromatids
as a result of replication during the S phase of the cell cycle.
Zygotene. The chromosomes begin to pair off. Pairs of chromosomes are called
homologous chromosomes, and this pairing process is exact.
Pachytene. The chromosomes contract due to repeated coiling. Crossing over
takes place during this stage where a segment of a sister chromatid of one
chromosome is exchanged with the same segment of the sister chromatid of the
homologous chromosome through the formation of a cross-linkage of the segments
called a chiasma (Figure 4). After crossing over, the sister chromatids of each
chromosome may no longer be identical with each other based on the genetic
material they contain.

325
Figure 4. Crossing over of homologous chromosomes during meiosis I.
Diplotene. The chromosomes begin to uncoil.
Diakinesis. The paired chromosomes disperse in the nucleus.
STAGE B: Metaphase I. The paired chromosomes arrange themselves along the
equatorial plate.
STAGE C: Anaphase I. Spindle fibers form and attach to the centromeres of the
chromosomes. The homologous chromosomes separate from each other completely
and start their movement toward the poles of the cells as they are pulled by the
spindle fibers. As the centromere of each chromosome does not divide, the sister
chromatids remain together.
STAGE D: Telophase I. This is the stage when the chromosomes reach their
respective poles. Cytokinesis follows and two daughter cells are formed. Each cell
now has only half the chromosome number because only one chromosome from
each pair goes to the daughter cell. This is called the haploid condition, in contrast
to the diploid condition at the beginning of meiosis I where each chromosome pair is
intact. Telophase I is followed by interphase II.

326
Note that each chromosome still has two sister chromatids; it is therefore
necessary for the cells to undergo another round of division.
The second meiotic division, also known as meiosis II, is mitotic in nature
and consists of the following stages: prophase II, metaphase II, anaphase II and
telophase II; these stages are identical with the mitotic stages. The results are four
cells, two from each daughter cell from meiosis I, with one half the diploid
chromosome number and with only one sister chromatid for each chromosome.
Figure 5 shows the different stages of meiosis in the squash anther.
Figure 5. Stages of meiosis in the squash anther.
_____________________________________________________
Activity 2
Comparing mitosis and meiosis
Objective:
By the end of the activity, you should be able to differentiate mitosis from
meiosis.

327
Procedure:
Complete the table below.
Mitosis Meiosis
Number of daughter cells produced
Number of chromosomes is halved.
(Yes/No)
Pairing of homologous chromosomes take
place. (Yes/No)
The daughter cells produced are always
identical in terms of genetic material.
(Yes/No)
_____________________________________________________
Role of Meiosis in Gametogenesis
Gametes such as eggs and sperms unite during fertilization, forming a diploid
zygote. The zygote has one set of chromosomes from the male parent and another
set from the female parent. In humans, both father and mother contribute 23
chromosomes each through their gametes. Thus, the zygote has 46 chromosomes.
The zygote divides many times. This produces a new diploid multicellular organism.
Sperm cells are produced in the testes of male animals. Meiosis produces
four cells which are very small but of similar size. These cells become spermatozoa
(singular form is spermatozoon) or sperms. The nucleus is found in the head of the
sperm; mitochondria are found at the midpiece that connects the head to the tail.
These mitochondria provide the energy for the movement of the sperm’s tail.
In female animals, egg cells are produced in the ovary. When a cell in the
ovary undergoes meiosis, new cells which differ in size are produced. After meiosis I,
two cells – one big and one small – are produced. Meiosis II produces one big and
one small cell from the first big cell. The small cell produced from meiosis I may or
may not divide. If it does, two small cells are produced. The big cell becomes the egg
cell; the small cells disintegrate. The egg cell contains a lot of stored food which is
used by the growing embryo at the start of its development. In fertilization, the tiny
sperm cell only contributes its genetic material found in the head. Figure 6
summarizes the formation of gametes.

328
Figure 6. Gametogenesis in the testis and ovary of animals.
When Something Goes Wrong During Meiosis
Meiosis may not always proceed normally. Accidents sometimes happen.
These accidents may affect the functioning of the spindle fibers or the movement of
one or more chromosomes. In humans, some accidents have been known to cause
abnormal conditions. For example, when chromosomes in a pair fail to separate from
each other during Meiosis I, the resulting gamete acquires both members of a pair of
chromosomes. If this involves chromosome pair 21, for example, and one of the
gametes contains two copies of the chromosome, then the individual produced will
have 47 chromosomes in his or her cells (with three copies of chromosome 21). This
condition is known as Down’s syndrome, named after Dr. Langdon Down who first
studied the condition. The extra chromosome 21 will lead to an imbalance of genetic
material in the cell. People with this condition suffer from variable degrees of mental
retardation, sterility, and increased risk beyond the age of 40 of Alzheimer’s disease,
which affects the functioning of the brain. Down’s syndrome is usually associated
with pregnancy in women above 35 years of age.

329
Sometimes, a piece of chromosome breaks off and gets lost. The effects of
this accident depend on the particular genetic material lost. For example, when a
part of chromosome 5 is lost, the afflicted individual will have a face that is round,
moonlike, cries feebly and is mentally and physically retarded. This condition is
called Cri du chat syndrome; cri du chat is French for cat’s cry, which is the sound
a baby with this condition makes when he/she cries.
Several drugs may cause breaks or other abnormalities in the chromosomes.
Chlorpromazine (a popular tranquilizer), diphenhydramine (an antihistamine), and
lysergic acid diethylamide or LSD (a hallucinogen) are some drugs known to cause
breaks in the chromosomes.
Mendelian Genetics
How is the behavior of the chromosomes during meiosis related to heredity?
In order to answer this question, we must first look back at the experiments of Gregor
Mendel. The results of his garden experiments laid down the foundations of Modern
Genetics.
Mendel’s Discovery of the Principles of Heredity
Gregor Mendel was an Augustinian monk in a monastery in Brünn, Austria-
Hungarian Empire (now Brno, Czech Republic). He was interested in investigating
how individual traits were inherited. He wanted to find out whether both parents
contributed equally to the traits of the offspring. He also wanted to know if the traits
present in the offspring were produced by the blending of the traits of the parents.
Mendel chose the garden pea (Pisum sativum) for his experiments. Before he
started his experiments, Mendel first produced pure-breeding plants. Mendel allowed
his pea plants to self-pollinate for many generations until all the offspring had the
same features as the parents, generation after generation.
When he has pure-breeding plants, Mendel began cross-pollinating peas with
contrasting traits. The pure-breeding peas constituted the parental or P1
generation. All offspring of these crosses resembled one another. For example,
when he crossed pea plants that produced round seeds with pea plants that
produced wrinkled seeds, all the offspring had round seeds.

330
The offspring of the parental cross are called the first filial (F1) generation.
In Mendel’s experiments, the F1 generation are also called hybrids because they
resulted from a cross between two pure-breeding plants with contrasting traits (for
example, pea plants with round seeds crossed with pea plants with wrinkled seeds).
Table 2 shows the seven pure-breeding crosses that he made based on seven
characters of the plant and the resulting traits of the F1 generation.
Table 2. Results of Mendel’s crosses between pure-breeding pea plants
Characters Studied Parents
First Filial (F1)
Generation
Seed shape Round Wrinkled Round
Seed color Green Yellow Yellow
Seed coat color Colored White Colored
Pod shape Inflated Constricted Inflated
Pod color Green Yellow Green
Flower position Axial Terminal Axial
Stem length Long Short Long
When the plants from the F1 generation were crossed with each other or self-
pollinated, the offspring (F2 or second filial generation) were of two types.
For example, Mendel counted 5,474 round seeds and 1,850 wrinkled seeds
in the F2 generation. Note that the round seeds were about three times as many as
the wrinkled seeds. The ratio of round seeds to wrinkled seeds was 2.96:1 or nearly
3:1. Moreover, the wrinkled seed type did not appear in the F1 generation. Table 3
summarizes the results on Mendel’s second set of experiments.

331
Table 3. Results of Mendel’s crosses between hybrid plants
Characters
Studied
Hybrid
F2 Generation Produced by
Self-Pollinating F1 Hybrids
Observed
Ratio
Seed shape Round Round Wrinkled 2.96:1
Seed color Yellow Green Yellow 3.01:1
Seed coat color Colored Colored White 3.15:1
Pod shape Inflated Inflated Constricted 2.95:1
Pod color Green Green Yellow 2.82:1
Flower position Axial Axial Terminal 3.14:1
Stem length Long Long Short 2.84:1
Based on the results of his experiments, Mendel hypothesized that there was a
factor in the plants which controlled the appearance of a trait. These factors are what
we call genes today.
Since two alternative expressions of a trait (e.g., round or wrinkled seed)
were possible, he hypothesized that traits were controlled by a pair of genes, now
called alleles. Mendel’s first hypothesis was: in each organism, there is a pair of
factors which controls the appearance of a particular trait.
Mendel noted that for each trait he studied, there is one trait that dominates
the other. Based on the results for the F1 generation, the trait for round seeds is the
dominant trait. The trait of wrinkled seeds, which did not appear in the F1
generation, is called the recessive trait. Its appearance was either prevented or
hidden by the dominant trait. This is now known as the principle of dominance: The
dominant trait dominates or prevents the expression of the recessive trait. Today,
dominant and recessive traits are represented by a capital and a small letter,
respectively. A dominant trait like round seed, for example, is represented by letter R
and a recessive trait like wrinkled seed is represented by a small letter r. Since
genes occur in pairs, a pure-breeding round-seed plant is symbolized as RR and
pure-breeding wrinkled-seed pea plant as rr. Table 4 shows the dominant and
recessive traits of peas studied by Mendel.

332
Table 4. Dominant and recessive traits in Pisum sativum (Garden Pea)
Characters Studied Dominant Trait Recessive Trait
Seed shape Round Wrinkled
Seed color Yellow Green
Seed coat color Colored White
Pod shape Inflated Constricted
Pod color Green Yellow
Flower position Axial Terminal
Stem length Long Short
Law of Segregation
Before Mendel’s time, it was believed that all traits become mixed when they
are transmitted from generation to generation, as red and blue paints mix to give a
violet color. However, when Mendel crossed pure-breeding pea plants, the pea
plants did not produce offspring with blended or intermediate traits.
In Mendel’s experiments, the pure-breeding parent plants had two identical
genes for a trait: round seed = RR, wrinkled seed = rr. Mendel hypothesized that:
The pair of genes segregate or separate from each other during gamete formation.
This is now known as the Law of Segregation.
Genes and Gametes
Following Mendel’s reasoning, a pure-breed, round-seeded parent plant has
an allelic combination or genotype of RR while a pure-breed, wrinkled-seeded
parent plant has a genotype of rr. Individuals that are pure-breeding for a particular
character therefore have identical alleles. These individuals have a homozygous
genotype. For seed shape, a homozygous dominant individual will produce round
seeds while a homozygous recessive individual will produce wrinkled seeds.
Mendel’s law of segregation states that the genes of a pair, for example RR,
separate during gamete formation. One gene goes to one gamete, while the other
gene goes to another gamete. Since the genes of this pair are alike, all the gametes
produced by this homozygous parent will be alike. All have gene R. The same is true
for the other parent. All its gametes will have gene r. (See Figure 7.)

333
Figure 7. Gamete formation of pure-breeding round- and wrinkled
seed-bearing pea plants.
Now recall what we have learned in meiosis. During anaphase I of meiosis I,
the chromosome pairs separate and move to opposite poles. Now remember that a
trait is governed by a pair of alleles. Each allele is found in a chromosome of a
chromosome pair. In other words, the chromosomes serve as vehicles for these
alleles. So when these chromosomes segregate during anaphase I, the alleles they
carry also segregate. This becomes the chromosomal basis of Mendel’s first law
(see Figure 8).

334
Figure 8. Chromosomal basis of Mendel’s Law of Segregation.
At fertilization, when the gametes formed during gametogenesis by RR and rr
plants unite, all the zygotes will have the genotype Rr (Figure 9). Thus, all the F1
plants will have a genotype of Rr. An individual with contrasting alleles (a dominant
and a recessive allele) for a particular character is said to have a heterozygous
genotype. However, Rr individuals will still produce round seeds because of the
presence of the dominant allele R. These will be just as round as all the seeds
produced by the RR parents. The expression of the genotype of an individual for a
particular character is referred to as its phenotype.

335
Figure 9. The result of crossing pure-breeding round and wrinkled seeds.
Knowing the Genotype
When you observe a pea plant, you can easily see the plant’s yellow pods or
its axial flower. By simply looking at the plant, you can immediately tell a plant’s
phenotype. However, you cannot always tell its genotype. For instance, a plant with
wrinkled seeds certainly has a rr genotype. But what about a plant with the dominant
trait, round seed? Its genotype could either be RR or Rr. There is, however, a way of
knowing whether the plant is homozygous or heterozygous for a given character.
Mendel applied two techniques in determining the genotype of a pea plant. These
are self-fertilization and testcross techniques.
1. Self-fertilization Technique
When self-fertilized, homozygotes always produce pure-breeding plants.
Thus, round-seeded peas will breed only round-seeded peas. What about
heterozygotes? Look at Table 3 again. Heterozygous round F1 peas produce round
and wrinkled seeds in the ratio three round seeds to one wrinkled seed. This ratio
(3:1) is called a phenotypic ratio.

336
Self-fertilization enables us to determine whether an individual is
homozygous or heterozygous for a given trait by observing the phenotype(s) of its
offspring. Homozygotes are pure-breeding. Heterozygotes produce two kinds of
offspring; three out of four offspring show the dominant trait and one out of four
excessive the recessive trait.
2. Testcross Technique
Testcross involves a cross between the recessive parental type (rr in our
sample cross) and the individual with the dominant trait but with unknown genotype.
You will observe in Figure 10 that homozygote dominants, when crossed with
recessives, produce only one kind of offspring and all exhibit the dominant trait.
Heterozygotes, on the other hand, when crossed with recessives, produce two kinds
of offspring. About one-half of the offspring show the dominant trait while the other
half exhibit the recessive trait.
Figure 10. Testcross technique.

337
Probability
Chance plays a role in the inheritance of a trait. During fertilization, the union
of a male gamete with gene R and a female gamete with gene r, for instance,
happens by chance. During meiosis, the assortment of the different chromosomes
also occurs by chance. Activity 3 illustrates the role of chance in the inheritance of a
trait.
Activity 3
Tossing coins and probability
Objective:
After performing this activity, you should be able to predict the outcomes of
crosses based on the principle of probability.
Materials:
2 coins, a piece of paper, and a pencil or pen
Procedure:
1. On a piece of paper, make a chart similar to the one given below.
Head (H) Tail (h)
Total
Percentage
Ratio of the combinations
2. Toss a coin. If a head comes up, mark column 1; if a tail, then mark column 2.
Make 50 tosses of the coin.
3. Get the total number of times each face of the coin appears. Calculate the
percentage of the appearance of each face. To compute the percentage:
(total / 50) x 100 %

338
Q1. What is the ratio of heads to tails?
4. Let us assume that the coin represents the genotype of a parent, and each face
is an allele, with the head as the dominant allele (H) and the tail as the recessive
allele (h).
Q2. What is the ratio of the gametes of this parent with heterozygous genotype?
5. On the same piece of paper, make a chart similar to the one given below.
Head-Head
(HH)
Head-Tail
(Hh)
Tail-Tail
(hh)
Total
Percentage
Ratio of the combinations
6. Toss the two coins together. If a head-head combination appears, mark column
1; if head-tail, mark column 2; and if tail-tail, mark column 3. Make 50 tosses of
the coins.
7. Get the total number of times each combination appears. Calculate the
percentage of the appearance of each combination. To compute the percentage:
(total / 50) x 100 %
Q3. What is the ratio of a head-head, head-tail, and tail-tail combination when you
make 50 tosses?
Q4. If you toss the same coins in 100,000 times, would you approximately get the
same ratio?
Q5. Let the head (H) represent a dominant gene and the tail (h), a recessive gene.
Compare the ratio you obtained in this activity with the one obtained by Mendel
in his monohybrid F2 generation peas (see Table 3). Are they approximately
similar?
_____________________________________________________

339
Diagramming a Cross
Mendel’s crosses can be recorded in a chart called a Punnett square. The
Punnett square helps us to predict the outcome of a given cross. It allows us to
determine the possible combinations of genes in a cross.
The use of the Punnett square can be best illustrated by solving an actual
problem, like determining the expected result when two hybrid round-seeded peas
are crossed. From previous discussions, you know that the expected phenotypic
ratio from this cross is 3:1. This time, we will determine the expected genotype of the
offspring.
Figure 11 diagrams the steps in making a Punnett square. From the finished
square, you can tell the genotypes of the offspring in the given cross.
Look at Figure 11. How many kinds of genotypes are possible in this cross?
What are these genotypes?
Since a zygote with a genotype Rr is shown twice in the Punnett square in
Figure 11, the chance or probability that a zygote will have an Rr genotype is two out
of four (2/4 or 50%). One out of four (1/4 or 25%) will have a genotype of RR while
one out of four will have a genotype of rr. Therefore, the genotypic ratio in the given
cross is one RR (homozygous round seed) to two Rr (heterozygous round seed) to
one rr (homozygous wrinkled seed). The genotypic ratio is simply written as 1:2:1.
This 1:2:1 ratio is what you should have obtained as your ratio in Activity 3.

340
Figure 11. Punnett square method to solve a hybrid cross.
Activity 4
Comparing genotypic and phenotypic ratios for a
typical Mendelian trait
Objective:
After performing this activity, you should be able to solve for the phenotypic
and genotypic ratios of any given cross.
R
r
Rr
Round Round
X
R r
gametes
gametes
Genotypic Ratio: ¼ RR: ½ Rr: ¼ rr
RR
Rr
Rr
Rr
Rr
(Male parent) (Female parent)
Phenotypic Ratio: ¾ round: ¼ wrinkled

341
Procedure:
Let D = dominant allele and d = recessive allele, while DD, Dd, and dd
represent the homozygous dominant, heterozygous dominant, and homozygous
recessive genotypes, respectively. For each type of cross, determine the genotypic
and phenotypic ratios, respectively. The first cross was already done for you.
Cross Genotypic Ratio Phenotypic Ratio
1. DD x DD 100% DD 100% dominant
2. DD x Dd
3. DD x dd
4. Dd x Dd
5. Dd x dd
6. dd x dd
This table summarizes the genotypic and phenotypic ratios of typical
Mendelian traits. Knowing the Mendelian genotypic and phenotypic ratios can make
solving genetic problems easier.
_____________________________________________________
Cross with Two Factors (Dihybrid Cross)
Mendel also studied the inheritance of two pairs of factors in an individual. A
cross between individuals that involve two heterozygous pairs of genes is called a
dihybrid cross.
Mendel crossed a plant with genotype RRYY (round, yellow seeds) and a
plant with genotype rryy (wrinkled, green seeds). The F1 peas exhibited the dominant
traits for the heterozygous genotype RrYy. Assuming Mendel’s Law of Segregation,
each pair will segregate during the formation of gametes. Each gamete will therefore
receive one allele from each pair. If the pairs of alleles are found on different
chromosomes, then each dihybrid will produce four different types of gametes with 1⁄4
probability each (Figure 12).

342
Figure 12. Gametes produced by a dihybrid genotype.
Self-fertilization of F1 peas produced four phenotypes. The phenotypes with a
ratio 9:3:3:1 are as follows:
9 (round, yellow seed)
3 (round, green seed)
3 (wrinkled, yellow seed)
1 (wrinkled, green seed)
Can you show, using a Punnett square, how this phenotype is obtained?
Activity 5
Filling up the Punnett square for a dihybrid cross
Objective:
At the end of this activity, you should be able to use a Punett square when
solving for dihybrid crosses.
Procedure:
Given the cross RrYy x RrYy, copy and fill up the Punnett square below.
Base your answers to the given questions on the completed diagram.
RrYy
Round, yellow seeds
RY Ry rY ry
¼ ¼ ¼ ¼

343
Q1. What are the male gametes? female gametes?
Q2. What proportion of the offspring will have the following phenotype: RY, Ry, rY,
and ry?
Q3. How many kinds of genotypes will the offspring have?
Q4. What is the probability that an individual will have a genotype of RRyy? RrYy?
Rryy? RRYY?
_____________________________________________________
Law of Independent Assortment
From the results obtained from his hybrid crosses, Mendel formulated his last
hypothesis: The distribution or assortment of one pair of factors is independent of the
distribution of the other pair.
The law of independent assortment explains why traits are inherited
independent of each other. The law applies to factors (or genes) that are found on
separate chromosomes. Since they are found on separate chromosomes, the
segregation of one pair of factors is not affected by the segregation of the other pair.
Therefore, their distribution in the resulting gametes will be at random (Figure 13).

344
Figure 13. Chromosomal basis of Mendel’s Law of Independent Assortment.
The Birth of the Science of Genetics
Mendel published his experimental results and analysis in 1866. However,
biologists of that time paid little attention to them. Nobody tried to repeat Mendel’s
experiments or to apply the techniques he used to study the different traits in other
organisms. For many years, Mendel’s results remained unnoticed. However, these
results were rediscovered independently in 1900 by three scientists, namely: Karl
Correns, Hugo de Vries, and Erich Tschermark von Seysenegg. Only then did the
scientific world come to know and benefit from Mendel’s findings.
This rediscovery marked the beginning of the analytical study of heredity. It
also gave birth to genetics as a new science, founded on Mendel’s findings. Genetics
also includes the study of genes and chromosomes and their properties and
behavior in cells, individuals, and the population.

345
Non-Mendelian Patterns of Inheritance
Are all traits controlled by a dominant or a recessive gene? What about traits
that have more than two phenotypes? Do they follow Mendelian patterns of
inheritance?
1. Incomplete Dominance
When a pure red-flowered four o’clock plant is crossed with a pure white-
flowered four o’clock plant, the offspring will produce neither red nor white flowers.
Instead, all flowers will be pink. In other words, the offspring will have a phenotype
intermediate between the phenotype of both parents. Such a phenomenon is called
incomplete dominance. This means neither of the two alleles is completely
dominant, and the heterozygous will be a new phenotype. Therefore, the genotypic
ratio also becomes the phenotypic ratio.
Activity 6
Phenotypes and genotypes in incomplete
dominance
Objective:
This activity will reinforce the genotypic and phenotypic ratios in a typical
incompletely dominant trait.
Procedure:
In four o’clock plants, R1 is the allele for red color and R2 is for white color.
Two pink flowered plants were crossed.
Q1. How many types of gametes will each parent produce?
Q2. What are the phenotypes of the offspring?
Another cross was made involving a red flowered plant and a pink flowered plant.
Q3. What would be the phentopytic and genotypic ratios of the offspring of this
cross?

346
2. Codominance
Another pattern of inheritance is codominance. This results when one allele
is not dominant over the other. The resulting heterozygotes exhibit the traits of both
parents. One example of codominance is the MN blood typing in humans.
On the surface of our red blood cells are proteins bound to sugar molecules,
forming complexes called antigens. One group of antigens are controlled by a pair of
alleles, LM
and LN
. The pairing of these alleles will determine the blood type of an
individual, and there are three: M, MN and N. Table 5 summarizes the genotypes
and phenotypes of the MN blood typing in humans.
Table 5. Human MN blood types and their genotypes.
Blood Types Genotypes
M LM
LM
MN LM
LN
N LN
LN
Note that in the heterozygote condition, both LM
and LN
alleles are expressed in that
the red blood cells will have the M and N antigens. Just like in incomplete
dominance, the genotypic ratio in codominance also becomes the phenotypic ratio.
3. Multiple Alleles
Sometimes, even if only two alleles control a trait, there may actually be more
than two types of alleles available. This will also lead to more than two phenotypes
expressed.
Another blood group system in humans, the ABO system, is an example of a
character governed by multiple alleles. Three alleles are responsible for this blood
system: IA
, IB
, and i. The ABO blood type is determined by the presence or absence
of two antigens, A and B. Allele i does not code for an antigen. There are four
possible blood types as shown in Table 6.

347
Table 6. Human ABO blood types and their phenotypes.
Blood Types Genotypes
A IA
IA
, IA
i
B IB
IB
, IB
i
AB IA
IB
O i i
The IA
and IB
alleles are dominant over the i allele, which is always recessive.
However, when the IA
and IB
alleles are inherited together, both alleles are expressed
equally. This also makes IA
and IB
codominants of each other.
Activity 7
Inferring genotypes of ABO blood types based on
the parental blood types
Objective:
By the end of this activity, you should be able to infer the unknown
phenotypes of individuals on the basis of the known phenotypes of their family
members.
Procedure:
Given the blood types of the mother and the child, identify the possible blood
types of the father.
Mother’s Blood Type Father’s Blood Type Child’s Blood Type
A A
B AB
AB B
O O

348
Sex Chromosomes and Sex Determination
Observation of the human body cells shows 23 pairs of chromosomes for
both male and females. 22 pairs are somatic chromosomes. The 23rd
pair consists of
sex chromosomes.
Human males and some other male organisms, such as other mammals and
fruit flies, have non-identical sex chromosomes (XY). Females have identical (XX)
sex chromosomes.
Let us study gamete formation based on the sex chromosomes. You will
observe in Figure 14 that all egg cells receive an X chromosome from a germ cell,
while half of the sperm cells receive X chromosomes and the other half receive Y
chromosomes.
If an egg is fertilized by a sperm with a Y chromosome, as shown in Figure
11, the offspring is male. When an egg is fertilized by a sperm carrying an X
chromosome, the offspring is female. Note that there is a 50 percent chance of
having a male or female offspring. The greater the number of offspring, the greater is
the chance of getting the expected 1:1 ratio of male and female.
Figure 14. Types of gametes produced based on the sex chromosomes in
humans and the ratio of the zygotes generated after fertilization.

349
4. Sex-Linked Genes
Genes located on the X chromosomes are called X-linked genes. Genes on
the Y chromosomes are called Y-linked genes.
An example of an X-linked trait in humans is hemophilia. A person suffering
from hemophilia could die from loss of blood even from a small wound because the
blood either clots very slowly or does not clot at all. Another example of X-linked trait
is color blindness.
To illustrate the inheritance of an X-linked trait, we will use color blindness in
our discussion. Study Table 7. The X chromosome with the gene for color blindness
is represented as XC
, while the one without is represented as X.
Table 7. Genotypes and phenotypes of color blindness in humans.
Genotype Phenotype
1. XX normal female
2. XXC
normal female, carrier of the gene
3. XC
XC
color blind female
4. XY normal male
5. XC
Y color blind male
Notice that for a female to become color blind, she must be homozygous
(XC
XC
) for the color blind genes. The trait is therefore recessive in females. If a
female only has one X chromosome with the allele for color blindness, she becomes
normal but can pass on the trait to her offspring. She is therefore a carrier for the
trait.
Since males have only one X chromosome, the gene for color blindness when
present in the male will always be expressed because it does not have an allele to
hide or prevent its expression. Thus, the male will be color blind. This is the reason
why color blindness is more common in males than in females.
An example of a Y-linked trait is hypertrichosis pinnae auris, a genetic
disorder in humans that causes hairy ears. Since the trait is found in the Y
chromosome, then only males can have the trait. A father who has the condition will
pass it on to all his sons, and they, in turn, will pass it on to their own sons.

350
References
Brooker, R.J. (2008). Genetics: analysis and principles (3rd
ed). Irwin/McGraw-Hill.
Klug, W. S., M. R. Cummings, and C. A. Spencer. (2007). Essentials of genetics (6th
ed). New Jersey, USA: Pearson Education, Inc.
Lewis, R. (1999). Human genetics: concepts and applications (3rd
ed).
WCB/McGraw-Hill.
Philippines. Department of Education. (2004). Biology: Science and
technology textbook for 2nd
year. (Revised ed.). Quezon City: Author.
Ramirez, D.A., Mendioro, M.S. and Laude, R.P. (2010). Lecture notes in genetics (9th
ed). San Pablo, Philippines: 7 Lakes Printing Press.

Grade 8 Learning Module in Science - Complete

More Related Content

What's hot (20)

Similar to Grade 8 Learning Module in Science - Complete (20)

Recently uploaded (20)

Grade 8 Learning Module in Science - Complete